
==== Front
Nutr Rev
Nutr Rev
nutritionreviews
Nutrition Reviews
0029-6643
1753-4887
Oxford University Press

38041551
10.1093/nutrit/nuad134
nuad134
Systematic Review
AcademicSubjects/MED00060
Why do mothers mix milk feed their infants? Results from a systematic review
https://orcid.org/0000-0002-1259-6505
Monge-Montero Carmen Department of Research, Monge Consultancy Food and Nutrition Research, Leiden, The Netherlands

van der Merwe Liandré F Danone Nutricia Research, Utrecht, The Netherlands

Tagliamonte Silvia Department of Agricultural Sciences, University of Naples Federico II, Naples, Italy

https://orcid.org/0000-0002-5006-0832
Agostoni Carlo Fondazione IRCCS Ospedale Maggiore Policlinico, Pediatric Clinic, Milan, Italy
Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy

https://orcid.org/0000-0002-6608-5209
Vitaglione Paola Department of Agricultural Sciences, University of Naples Federico II, Naples, Italy

Correspondence: C. Agostoni, Fondazione IRCCS Ospedale Maggiore Policlinico, Pediatric Clinic, Via della Commenda 9, 20121 Milan, Italy. E-mail: carlo.agostoni@unimi.it.
10 2024
01 12 2023
01 12 2023
82 10 13551371
© The Author(s) 2023. Published by Oxford University Press on behalf of the International Life Sciences Institute.
2023
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence (https://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reproduction and distribution of the work, in any medium, provided the original work is not altered or transformed in any way, and that the work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

Abstract

Context

Combining or supplementing breastfeeding with formula feeding, also called mixed milk feeding (MMF), is a common infant feeding practice. However, there is no well-established MMF evidence-base for informing and guiding parents. A better understanding of the reasons why mothers practice MMF may facilitate identification of efficient strategies for supporting exclusive breastfeeding, and/or opportunities to prolong breastfeeding, at least partially.

Objective

An updated systematic literature review was undertaken with the primary aim of gaining a deeper understanding of the reasons why mothers choose MMF.

Data Sources

Six databases were searched for relevant articles published in English from January 2012 to January 2022.

Data Extraction

Two reviewers independently performed the screenings and data extraction, and any differences were resolved by a third reviewer. Data from 138 articles were included, 90 of which contained data on MMF reasons/drivers, and 60 contained data on infant age and/or maternal demographic factors associated with MMF.

Data Analysis

A total of 13 different unique MMF drivers/reasons were identified and categorized according to whether the drivers/reasons related to perceived choice, necessity, or pressure. Risk of bias was evaluated using the Quality Assessment Tool of Diverse Studies and the JBI Systematic Reviews tool. Several different terms were used to describe and classify MMF across the studies. The most commonly reported reasons for MMF were related to a perception of necessity (39% of drivers, eg, concerns about infant’s hunger/perceived breast milk insufficiency or breastfeeding difficulties), followed by drivers associated with perceived choice (34%; eg, having more flexibility) and perceived pressure (25%; eg, returning to work or healthcare professionals’ advice). This was particularly true for infants aged 3 months or younger.

Conclusion

The key global drivers for MMF and their distribution across infant age and regions were identified and described, providing opportunities for the provision of optimal breastfeeding support. A unified definition of MMF is needed in order to enable more comparable and standardized research.

Systematic Review Registration

PROSPERO registration no. CRD42022304253.

breast-feeding
consumer behavior
infant feeding
mixed milk feeding
mothers
Danone Nutricia Research 10.13039/100015766 Ministry of Health 10.13039/100009647
==== Body
pmcINTRODUCTION

Breastfeeding (BF) is universally recognized for its benefits to mother and child, and the World Health Organization therefore recommends exclusive BF (EBF) for the first 6 months after birth, with introduction of complementary foods and continued BF thereafter.1 Despite the recommendations for EBF, global EBF rates remain low.2 Many mothers feed a combination of both breast milk and infant formula for variable durations. This feeding method, also called mixed milk feeding (MMF), is a common infant-feeding method practiced around the world. Its global prevalence has been estimated to lie between 23% and 32% in the first year of life.3 Some studies have found rates of up to 50% or higher,4,5 and rates appear to be increasing in middle- and high-income countries.6–11

Despite MMF being a very common way to feed infants, there is no established MMF evidence base for informing and guiding parents. Mothers giving MMF have described feeling isolated, confused, and as if they do not fit in anywhere12; moreover, a systematic literature review found that these mothers had a 6 times higher risk of experiencing guilt around their choice of feeding method than mothers who practice EBF.13 In the UK, 33% of midwife students reported having insufficient practical experience for supporting women who breast- and bottle-fed.14 While every effort should be taken to support and promote EBF for its undeniable benefits, the UNICEF UK Guide to the Baby Friendly Initiative Standards emphasizes that, when EBF is not possible, continued BF is important, even if partial.15 By supporting mothers who practice MMF to continue BF, and to meet their BF goals rather than transitioning fully to formula feeding (FF), there may be opportunities to support and increase babies’ exposure to breast milk and its benefits.7 Understanding the reasons why mothers practice MMF may be helpful for finding efficient strategies for supporting BF. By exploring the reasons mothers give for supplementing their breast milk, and the self-reported drivers for MMF, light may be shed on their feeding choice and the main factors that, for these women, stand in the way of giving EBF. Depending on the factors and drivers involved, MMF may offer some mothers a way to continue BF rather than switch to full FF, or even the opportunity of a return to EBF.16

In a previous meta-analysis and systematic literature review on MMF prevalence (the primary outcome), practices, and drivers (secondary aims), 79 articles were found that mentioned the reasons reported by mothers for providing their infants with MMF.3 The current study aimed, as a primary objective, to gain a deeper understanding specifically of the reasons why a mother chooses to combine or supplement her breast milk with FF. Therefore, the primary objectives of this study were to update the MMF drivers’ section of the existing systematic review with additional recent data (including reasons for practicing MMF in the first days after birth), and to conduct an analysis and interpretation of the identified MMF drivers. The secondary objective of this review was to describe the demographic characteristics of MMF mothers and their infants.

METHODS

Literature search

For the search, MMF was defined as feeding through a combination of BF and FF during the same period, irrespective of the number of feedings or the quantities of each. This definition allowed us to capture articles specifically addressing the feeding of a combination of human and formula milks, irrespective of other foods and/or fluids given. The systematic review was conducted following the recommendations and standards set by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).17 A prospectively developed protocol for the systematic literature review was registered in the International Prospective Register of Systematic Reviews (CRD42022304253).

Data sources

A systematic search was performed using the following databases: Cab Abstracts, BIOSIS Previews, British Nursing Index, Embase, Medline, and Social SciSearch. Articles from the last decade (from January 1, 2012 to January 14, 2022) were included to capture more recent data reflecting the context of parenting in the last 10 years and to complement and compare these data with the data already studied in our previous review (which focused on the period 2000–2018).3 A predefined search strategy was used with terms relevant to MMF drivers (please see the Supplementary Methods in the Supporting Information online). The last search was performed on January 14, 2022.

Study selection

A PICOS sequence with a priori inclusion and exclusion criteria (Table 1) was used to identify potentially relevant studies.18 Publications containing data regarding maternal drivers/reasons to MMF were included, as well as those including data regarding MMF population sample-size, infant age and gender, and/or maternal demographics (including age, parity, type of delivery, education, employment, and/or household income).

Table 1 PICOS criteria for inclusion and exclusion of studies

Parameter	Inclusion criterion	Exclusion criterion	
Population	Any populations of parents/caregivers giving, intending to give, or having given MMF to their infant. Parents of any age, race, and socio-economic status. Healthy term infants aged 0 mo to 2 y, receiving MMF for any range of time, born to mothers from any social class, age, race, and nationality and living within common local settings	Nonhuman studies and studies that concerned diseased or ill adults (eg, those with HIV) or infants, preterm (gestational age <37 wk) infants, or children >2 y old. Studies under special conditions (refugees camps, preterm, HIV, extreme poverty, emergency situations)	
Intervention	MMF refers to the combination of BF and FF during the same period, irrespective of the number of feedings or quantities (either of BF or FF)	MMF methods that did not fulfil our definition of MMF (eg, mixed feeding with food/milk); studies with only BF and/or FF; and studies not providing MMF information	
Comparison	No comparison criteria were applicable	No comparison criteria were applicable	
Outcome measures	MMF drivers, quotes of mothers practicing MMF related to their reasons for MMF, and association with maternal and infant demographics	MMF outcomes not related to MMF drivers or demographics	
Study design	Cross-sectional, cohort studies, case series, randomized controlled trial studies, meta-analyses, systematic reviews	Case–control studies and case reports	
Abbreviations: BF, breastfeeding; FF, formula feeding; MMF, mixed milk feeding; mo, months.

In order to ensure the generalizability of the systematic review findings to the actual population of interest, specifically MMF mothers, the external validity of all the studies included in the studies was assessed. This evaluation involved reporting relevant aspects of the studies, such as participant characteristics concerning baby age, country, and study type, as well as sample size and details of the description of the feeding type. All of this information is reported in Table S1 (please see the Supporting Information online). Those studies in which a particular type of population or setting was specified (eg, natural disasters, ill mothers, or extreme living conditions) were excluded. In this way, the findings of the included studies could be assumed to be generalizable to the intended population.19

Data extraction

The relevance of each identified publication was assessed through 3 steps. First, the citations were screened, and those studies that appeared not to be relevant (eg, nonhuman studies) and duplicates were excluded. Thereafter, the titles and abstracts were independently screened for eligibility by 2 individual reviewers. For those studies meeting the inclusion criteria, full texts of the articles were retrieved and assessed separately by the same 2 reviewers. A third reviewer was consulted to resolve any differences of opinion between the first 2 reviewers in both of these screening phases. Finally, the first 2 reviewers extracted all the relevant data from the included articles, and the third reviewer assessed the accuracy of the extracted data by cross-checking the data on MMF drivers, demographics, and infant characteristics against the sources. The information gathered from each study included: study location (country), MMF prevalence, population sample size, age of the infants, MMF drivers and practices, and maternal demographics data. The latter included maternal age, infant sex (percentage of boys in the sample), type of delivery (percentage of vaginal deliveries in the sample), maternal education (percentage of mothers with a university degree or higher in the sample), maternal employment (percentage of working mothers in the sample), and parity (percentage of primiparas in the sample). If a study reported only a range of ages and not the mean age of the infants, the highest age of the range was used (eg, if the drivers/demographics data of MMF were provided for the period 3 months–6 months or 0 months–6 months, the age was considered as 6 months in both cases). When dealing with intervention studies (eg, randomized controlled trials), only data from the control groups were extracted to avoid intervention bias. Demographic data for both the MMF mothers and the total study population were extracted.

All extracted MMF drivers were summarized, grouping them according to the reason mothers gave for providing or planning to provide MMF, as described in the eligible literature sources. Only the drivers specified for giving MMF were considered, and these were obtained from the articles in which they were identified and distinguished from EFF and EBF drivers. Some MMF drivers were extracted by summarizing mothers’ quotes regarding their feeding or MMF practices/drivers at various moments or in various situations during the day, as noted in focus groups or other qualitative research settings.

Analysis and synthesis strategy

The resulting extracted drivers were subsequently divided into subcategories using a qualitative approach based on the results of the previous review. Individual reported reasons for MMF were qualitatively assessed for whether the motive suggested (a) a mother’s perceived necessity to start MMF, eg, due to BF difficulties or worries about her infant’s hunger; (b) a perceived pressure to start MMF due to external factors, eg, expectations from family/peers or a return to work; or (c) a choice by the mother to start MMF without any (perceived) obligation or obvious objective need, eg, for convenience or flexibility reasons. The number of mentions of each specific reason (corresponding to the number of articles reporting each reason at least once) was counted, the numbers for each subcategory were totaled, and the results are shown graphically for each of the 3 main categories. As the mothers’ motivations for MMF may differ depending on the age of their infant or their cultural background, the reasons provided by mothers for MMF were also summarized according to infant age (maternal feeding intention before birth, maternal feeding of infants aged 0 months to ≤3 months, and maternal feeding of infants aged >3 months to 6 months) and the geographical region (America [both North and South], Europe, Asia, Oceania, and Middle East/Africa). Articles in which the age of the infants was insufficiently specified were not included in these results (eg, articles including infants aged 1 month–12 months). Demographic data for both the MMF populations and the total studied populations were descriptively summarized into ranges, means ± standard deviation, and medians, and shown side by side. No weighting of data or statistical testing was carried out on the demographic data.

Quality assessment

The internal validity of all eligible studies was examined using the Quality Assessment with Diverse Studies (QuADS) tool.20 The coding criteria for the quality scoring of the selected studies are listed in the Supporting Information. The tool consists of 13 items designed to critically appraise the quality of each study by means of a 4-point scoring system (0, 1, 2, 3); a higher score total, calculated by the sum of scores given for each of the 13 items, translates into a higher-quality study, with a maximum value of 39. QuADS is not suitable for quality assessment of literature reviews, which were not previously assessed for risk of biases; therefore, the quality of the 3 included literature reviews was evaluated using the critical appraisal tool developed by the JBI for systematic reviews.21 This tool consists of a checklist by which systematic reviewers are guided in determining whether or not the published review article should be included in their review.

Changes from the previous systematic review

In our previous related review, our secondary aim was limited to describing MMF drivers (and practices). Although demographic variables were captured by default in the previous systematic review (due to our including articles mentioning MMF prevalence), including articles listing MMF-related demographic variables did not represent an aim in itself.

In updating the MMF drivers’ section of the systematic review, the following changes in methodology were implemented.

Our earlier review included articles published between 2000 and 2018 (see Figure S1 in the Supporting Information online), whereas the current systematic review included articles published between 2012 and 2022, to include the most recent data available on reasons that mothers practice MMF. In addition, the exclusion criteria were adjusted, by removing the exclusion criterion concerning articles addressing MMF between 0 hours and 72 hours after birth and adding the exclusion criterion concerning “articles published in languages other than English”. Our previous systematic review included articles published in Spanish and Chinese, due to the available language skills of the previous review team.

Previously the drivers were listed in one large overview of main reasons; in that review, they were classified according to mothers’ feelings of perceived necessity, pressure, or choice. In the current review, the extracted maternal demographic variables potentially associated with MMF were also listed and descriptively compared with the demographic variables for the total population of the mothers included in each article.

There were some differences between the search strategy used in the previous review and that used in this one. First, the search string was improved so that more relevant articles could be found (eg, by including terms such as “human p/0 milk”, “formula”, and “breastfed”, and including p/1 instead of p/0 in case there were additional words between the combinations of our selected keywords); second, some terms were excluded from the search so that the results could be narrowed down more effectively. Finally, for this systematic review one of the databases used in the last systematic review (PsycInfo) could not be accessed, and one additional database (Cab Abstracts) was included.

For the previous systematic review, it was not possible to find a suitable tool for assessing the quality of the studies related to the MMF drivers, and we focused our quality assessment on those articles relevant to our primary objective, evaluating global MMF prevalence. For the current systematic review, we assessed the quality of the different types of studies (qualitative and quantitative), using the Quality Assessment Tool of Diverse Studies (QuADS)20 and the JBI questionnaire for Systematic Reviews.21

Similar MMF driver/reason descriptions to those in the previous review were used, but some of the wordings and combinations were adjusted to reflect the current findings and to improve on clarity and accuracy. In addition, a new categorization were applied as described above, whereby drivers were divided into reasons associated with either (perceived) necessity, pressure, or choice (Table 2).

Table 2 MMF drivers categorized, and subcategories of the rearranged drivers found in the previous review3

	

RESULTS

Search and selection results

The initial search identified a total of 2262 items. Of these, 2098 were screened by title/abstracts, and thereafter 489 full-text articles were evaluated. After full-text screening, 125 articles were included and 358 articles were excluded from the search, and the reasons are listed in Figure 1.

Figure 1 Flow chart of search and selection process.  a Twelve articles included both MMF drivers and demographic data. As there was an overlap, these articles were not counted separately. MMF, mixed milk feeding

Of the 125 relevant articles included, 79 contained data on reasons/drivers for giving MMF. These data comprised a combination of qualitative and quantitative results, and quoted comments of mothers recorded during explorative or qualitative studies. Ten further articles were included that contained MMF driver data that were not captured by the current search but which were included in our previous systematic review and remained eligible for inclusion.22–31 This discrepancy between the search results was a result of changes to the wording applied in the search string (which were intended to reach more relevant articles) and changed access to various databases (further explained in the earlier section “Changes from the previous systematic review”). From the database searches, 89 articles (79 from new search + 10 from the previous search) were finally included, and 1 further relevant article was included that was retrieved via a web search.32 In total. 90 articles were therefore included in the analysis of MMF drivers and motives.

Regarding MMF maternal and infant demographics, 58 articles were found describing 1 or more of the demographic characteristics mentioned in the “Methods” section. In addition, 2 articles found via a web search,26,27 were included, totaling 60 articles.

Study design and characteristics of the reviewed studies

In total, 138 publications were included in this study, 90 of which included data describing MMF drivers/reasons, and 60 of which included data on maternal and/or infant demographics, with an overlap of 12 articles reporting both types of data. Key study and subject characteristics are reported in Table S1 in the Supporting Information online. Most of the studies were cohort (44.2%), cross-sectional (28.3%), and qualitative (20.3%) studies; the remaining studies were case–control studies, literature reviews, or randomized controlled studies. Data were obtained representing 43 countries in 5 regions: America (North and South, 41%), Europe (24%), Asia (22%), Middle East/Africa and Oceania (13%).

The terms used in the selected publications to describe and classify what we term MMF varied broadly between authors. The most used terms where “mixed feeding” (34.3%), “supplementary feeding” (19.1%), “partial BF” (10.9%), and “combination feeding” (10.9%). Several articles used multiple terms to describe this same feeding method (13.1%), while others did not use any specific term for MMF, instead describing the feeding method as “BF and FF” (13.4%). Terms were not found to be associated with specific regions, except for 1 term that was used specifically in America (especially in Latin-American communities), where some mothers referred to MMF as “las dos” or “both.”33–35

Critical appraisal of identified evidence results

The quality appraisal scores for each study are reported in Table S3 in the Supporting Information online. Scores ranged from 12 to 38, with a mean ± standard deviation (M ± SD) quality score of 27.3 ± 6.1 (out of a maximum of 39). Overall, the studies had good (at least 2 points out of a maximum of 3 points) theoretical or conceptual underpinning (with a M ± SD of 2.5 ± 0.7), provided a description of the target population and setting (M = 2.4 ± 0.7), provided good justification for the data collection tools used (M = 2.1 ± 0.8), and selected appropriate analytic methods (M = 2.1 ± 0.9). The study designs (M = 2.2 ± 0.6) and data collection tools used (M = 2.1 ± 0.8) were also deemed adequate for tackling the research aims. The evidence for consideration of the research stakeholders in the research design was, in contrast, found to be low in all of the studies (M = 0.5 ± 0.8). The results for the quality appraisal of the systematic review articles as analyzed using the JBI tool by Aromataris et al are in the Supporting Information. The 3 systematic reviews articles were approved by the authors.

Drivers/reasons for mixed milk feeding

Our search resulted in the inclusion of both quantitative (n = 28) and qualitative (n = 110) research articles. For the quantitative research articles, the MMF drivers were extracted from the relevant Results sections. For the qualitative research articles, information was extracted from both the Results sections and from the mothers’ own reported descriptions of their MMF views and experiences. There were 26 articles that included quotes from mothers about the reasons why they practiced MMF. The quotes were analyzed and categorized for each category of driver.

Categories of MMF drivers/reasons

Perceived necessity

This category included those drivers for which MMF was reported as if seen as a necessity, eg, to relieve the mother’s BF difficulties.25,29,35–61 The drivers reported in this category were also the most-reported drivers overall (Figure 2). The mother’s perception that her infant is hungry and/or self-perceived breast milk insufficiency was the most cited driver, being reported as a driver in 42 articles (Figure 2).22,24–26,29,30,38,44–51,53–57,60–81 In addition, drivers such as concerns around the infant’s health or size, or maternal exhaustion were widely reported.29,39,47,53,56,60,61,76,78,82–87

Figure 2 Bar-plot showing how many articles mention the specified driver at least once, presented according to MMF driver category; percentages in parentheses indicate the percentage of articles included in the review that mention the specified driver. BF, breastfeeding; BM, breast milk; MMF, mixed milk feeding

Perceived pressure

In this category, drivers were included that could be associated with a (perceived) maternal pressure experienced due to external factors. The most-reported driver in this category was the mother’s return to work, reported in 19 articles, followed by the advice of healthcare professionals (n = 18 articles). Finally, the perceptions of family, peers, and other external sources reportedly influenced the mother to choose MMF as a feeding method (Figure 2).

Perceived choice

This category of drivers captured those drivers suggesting that the mother chose to start MMF without any obvious perceived obligation or objective need; it was represented in 56 articles reporting drivers such as the perception that MMF contributes to the infant sleeping better, contributes to an improvement in family relationships, gives social flexibility, gives convenience, has the advantage of others being able to feed the infant, and supports the infant’s nourishment (Figure 2). This last driver was related to, eg, the intention of the mother to continue BF because of its unquestionable associated health and other benefits, while introducing FF for other reasons like being more convenient. This is supported by the study by Radzyminski and Callister,83 which indicated that MMF mothers claimed that positive benefit to the infant was the reason why they kept BF, but that MMF was easier than BF alone.82 The most commonly reported drivers in this category were the aims of “supporting the infant’s nourishment” or achieving a “complete nutrition,” followed by “the desire to have more flexibility” and “convenience”.

The proportions of articles reporting each category of MMF driver are presented, by geographic region and infant age, in Figure 3. Simple comparisons did not indicate obvious differences in the distribution of MMF drivers between the regions. However, perceived necessity, sometimes together with perceived pressure, were the predominant categories of drivers for every region.

Figure 3. (a) Bar-plot showing how many articles mention the specified MMF driver category for each region of residency; the percentages in parentheses indicate the number of articles that mention the specified driver category as a percentage of the total number of the included articles that provide data for each region. (b) Bar-plot showing how many articles relate the specified MMF driver category to mother’s feeding intention or baby age; the percentages in brackets indicate number of articles that mention the specified driver category in relation to feeding intention or baby age as a percentage of the total number of the included articles that provide data on feeding intention or baby age. MMF, mixed milk feeding

MMF drivers differ across the regions of the world. For almost all the regions, the dominant subcategory was perceived necessity (37% drivers per region), except for Asia and America, in which perceived necessity and perceived choice ranked similarly (37% and 38%, respectively). In Europe, America, and Asia, drivers related to perceived pressure (28%, 38%, and 37%, respectively) were reported in higher proportions than drivers related to perceived choice (26%, 23%, and 22%, respectively). Finally, perceived choice and perceived pressure were ranked the same for Oceania, and Middle East/Africa, and similarly for Europe (27%, 27%, and 29%, respectively).

However, when drivers were compared for a particular infant age category, a clear difference was noticed: drivers associated with “perceived necessity” were mostly reported in relation to younger infants (aged up to 3 months), whereas drivers associated with “perceived pressure” were more frequently reported during pregnancy and by mothers of infants older than 3 months. Table S2 in the Supporting Information online presents a matrix indicating links between the articles that mention MMF drivers in different regions and for different baby ages, which shows that most of the articles for all of the regions related to babies aged 0 months–3 months.

Description of maternal and infant demographics

Table S3 in the Supporting Information online shows the demographic characteristics of MMF and EBF women and infants reported in 60 publications from 24 countries. Figure 4 shows a graphical summary of these findings. In these articles, the reported MMF prevalence ranged from 6% to 77%, with an unweighted average of 34 ± 16%, and a median of 31%, while the EBF prevalence ranged from 7% to 85%, with an unweighted average of 43 ± 19%, and a median of 41%. MMF mothers’ ages ranged from 26 years to 36 years, and the EBF mothers’ ages ranged from 25 years to 33 years. Both feeding groups had an unweighted average age of 31 ± 2 years, and a median of 31 years, which was similar to the maternal ages in the total sample (unweighted average 30 ± 2 years, median 30 years).

Figure 4. Descriptive comparison between MMF, EBF, and total sample demographics, showing the prevalence of MMF and EBF, and maternal demographic data expressed as a percentage for each characteristic in the given population. a“% highest household income” means the highest income of the MMF mothers as a percentage of the highest household income in the total sample. b “% with a degree or higher” means the percentage of MMF mothers who had a degree or higher as a percentage of the number in the total sample who had a degree or higher. EBF, exclusive breastfeeding; MMF, mixed milk feeding

Regarding parity, slightly more MMF mothers were primiparas (unweighted average 46 ± 18%, median 49%) than among EBF mothers (unweighted average 43 ± 17%, median 42%) or among the total population (unweighted average 45 ± 15%, median 47%). Regarding the educational status of MMF mothers, data from 13 studies showed that, on average, 55 ± 11% of MMF mothers had at least a university degree or higher, compared with 59 ± 11% of the EBF mothers and 49 ± 12% of the total population (see Table S5 in the Supporting Information online).

The distribution of the demographic factors in Figure 4 suggests slightly greater household income and education level in EBF mothers compared with MMF mothers, and in MMF mothers compared with the total population. This suggests that MMF was slightly more common than EBF in middle-income groups, but less common than EBF in low-income groups. It is important to notice that in the 3 articles in which the MMF mothers were in the low-income demographic, their major focus was on household income. MMF mothers were observed to be less well educated than EBF mothers, but more educated than the total population. A larger percentage of MMF mothers were employed, compared with EBF mothers and compared with the total population in the included articles.

Differences in findings between the original and updated reviews

In this new review, several improvements have been introduced. First, the MMF drivers have been updated, encompassing those present in more recent publications, including those related to MMF during the initial days after birth, which were previously overlooked. Second, a comprehensive analysis and interpretation of the drivers has been conducted, addressing a gap that was present in the initial review. Finally, the review now includes detailed information on the demographic characteristics of the MMF mothers and their infants. Although the 2 studies differ slightly in their search strategies, it was possible to compare the main outcomes and thus to obtain an overview of the potential changes in MMF drivers since the earlier review.

For our previous review, 70 articles were identified that provided information on MMF drivers (see Figure S1 in the Supporting Information online). Of those articles, only 31 were published between 2012 and 2022. The current search captured 21 of these, while the other 10 articles were excluded from the current search due to changes in terms in the search string (eg, changes that excluded articles mentioning only EBF in the Abstract) and the omission of 1 database that was used last time (PsycINFO). Of the 21 articles captured in the current search, 3 were not considered relevant for the present review because they did not clearly focus on drivers for MMF specifically.

Figure 5 shows the repartition between the 2 reviews of the MMF drivers reported. The light gray bars show the drivers reported in the previous MMF review (of articles published between 2012 and 2022), and the dark grey bars show the new findings in the current systematic review.

Figure 5 Main drivers for MMF in a multiregional global context, from 90 articles from the years 2012–2022. The number on each bar is the number of articles mentioning that specific driver at least once in an article. BF, breastfeeding; BM, breast milk; MMF, mixed milk feeding

DISCUSSION

This systematic review provides an update of the evidence as well as a structured, in-depth overview of insights around maternal MMF drivers. By categorizing maternal reasons for MMF according to the presumed underlying perceptions of necessity, pressure, and choice, it was possible to describe and discriminate the different global MMF drivers and their relative frequency of reporting.

Insecurities and difficulties around BF were consistently found to be the drivers of MMF reported with the highest frequency in both this and our previous review. Mothers’ insecurities about whether their infant’s needs are being satisfied by their breast milk alone is, therefore, indicated to be a key reason for mothers to introduce MMF rather than EBF, particularly when it concerns infants aged 3 months and younger. Despite weak correlations being found between perceived and clinical milk insufficiency,88 infant nourishment concerns—as a driver for MMF—appear to be universal and widespread. These concerns, as well as the mother’s decision to practice MMF, may sometimes lead to profound emotional effects on mothers. In a Polish study, maternal concern about their infant’s hunger was found to be one of the predictors—for MMF mothers specifically—of developing postpartum depressive symptoms.89 At the same time, as highlighted earlier, mothers who provide supplemental FF are at much higher risk of experiencing feelings of guilt about their feeding method than mothers who practice EBF. In a UK study, it was found that feelings of guilt in MMF mothers could be traced to internal factors in over half of the cases (50.9%), rather than external factors in the environment (20.5%).90 Studies suggest that, particularly when BF intentions are unmet, guilt is experienced more frequently in mothers who practiced MMF compared with those who practiced EBF.13

There is a clear need for parental feeding support addressing the above-mentioned concerns. Providing reassurance to mothers could be especially relevant when BF or MMF support is given. In some cases, for instance, mothers have been found to be following unreliable cues or interpretations when assessing infant satiety vs hunger, and milk production sufficience vs insufficiency, leading to poor responsive feeding practices and supplementation with formula.24,39,91 This suggests that responsive milk feeding support, addressing mothers’ interpretations of and responses to infant cues, may be crucial for mothers in their management or prevention of perceived breast milk insufficiency and subsequent FF introduction.92 A previous study found that, especially in non-EBF and first-time mothers, as well as in those with depressive symptoms, advanced maternal age, or with infants who are becoming underweight, there is a need for educating mothers on responsive feeding.93 Other studies have also found that education around infant cues and responsive feeding can help to reassure mothers and increase their BF self-efficacy and durations.94–96 Such education on infant milk feeding cues may provide valuable reassurance and support the BF mother to have confidence in her ability to meet her infant’s needs. In some cases, it could mean more sustainable EBF, and in others it may even help mothers to move back to EBF after a brief period of MMF.6,45,97

Culture and culture-related conditions play an important role in infant feeding choice. For instance, Hispanic mothers tend to use MMF more due to acculturalization, and see MMF as the norm (called “las dos” or “both”).34,45,71,82 Many of them choose BF, because in their countries EBF is more common, as it is in many low-middle income countries,33,98 sometimes due to high formula prices.99,100 In addition, Latin-American and African-American mothers in the USA tend to be from low-income households and have lower education.25,47,62,64,66,101 In the USA, the more widespread use of formula may be due to the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) and the lower cost.34,57,76,82,86,102,103 In contrast, mothers with higher education104 and those not entering WIC programs more frequently choose MMF. This same result was found by Henninger et al, and even these MMF mothers introduced FF later.105

The data were sorted into 3 groups depending on infant age at the time of the interviews or during the period when the infant was receiving MMF. Pregnant mothers present different drivers than mothers who have given birth. The main reasons mothers stated for planning to practice MMF for their babies after birth were social flexibility, convenience reasons, to allow others to feed the infant,10–12 supporting the infant’s nourishment,10,12 and healthcare professionals’ advice,28,37,106,107 while recognizing the benefits of BF as well.28,37,43,106 Lastly, some mothers considered MMF as a convenient method for weaning,30 in case of emerging BF difficulty,37 or even as a possible way to prolong BF instead of just switching to FF.29,75

As part of our previous systematic review, MMF drivers in the first 72 hours post-partum were not considered, since it was suspected that the decision to practice MMF in these cases was not made entirely by the mother. In this review, it was found that in many articles the decision to practice MMF directly after birth was the mother’s decision, due to the perception that the baby was hungry, or concerns around breast milk sufficiency.44,46–48,51,52,54,55,58–61,62,63,74,76 Healthcare provider advice was a common driver during hospital stays, and this driver was categorized as a feeling of external pressure, since in some articles mothers refer to this driver as “doctor’s order” or “doctor’s advice.”58,106 In addition, in some cases the advice from the healthcare provider was given after the hospital stay, and it was given by the midwife and/or the physician.29,49,56

Most of the articles reported on early MMF of babies of ≤3 months but >72 hours, and the main driver category was perceived necessity. For the late MMF cluster (>3 months and ≤6 months), the main category was perceived pressure. This was expected as, in most of the countries, maternity leave finishes after 3 months post-partum, so mothers have to return to work or feel the pressure from the expectations of family and peers.22,31,53,73

Although drivers that were associated with a perceived necessity were reported with the greatest frequency (39%), drivers associated with perceived choice (34%) and pressure (25%) also made a substantial contribution to reported MMF motives. The reasons for MMF are diverse, and in order to provide the right support, the mother’s specific situation, including her motives for MMF and the internal and external factors at play, should be taken into account. For instance, when mothers decide to practice MMF as a way to relieve pressure when returning to work, BF-supportive conditions such as flexible working hours, adequate maternity leave, and BF facilities can help to reduce BF barriers.107 In some cases, infants are supplemented with formula due to health reasons, even if debatable, such as presumed weight loss44,63,74; only the official WHO growth charts should be used as a reference. Often, not only mothers, but also healthcare professionals, ignore the fact that the capacity of BF mothers is limited to 700 ml–800 ml of breast milk for the first 5 months–6 months of life, and advise disproportionate volumes of FF to be given.108–110

A striking finding from this updated review was that some mothers exchanged EBF for MMF due to COVID-19 concerns,111,112 despite the clinical evidence showing the benefits of EBF, even in mothers positive for COVID-19.113 In addition, Zanardo et al (2021) showed that higher maternal anhedonia and depression during the COVID-19 pandemic were associated with higher rates of MMF and FF than EBF practices in mothers who tested negative to COVID-19.114 Once more, lack of support and of correct information for mothers, along with family pressure at home during the pandemic,32 may have greatly contributed to the switch. The present rapid changes in the socio-economic and cultural context may further contribute to a sense of “self-isolation” for mothers, who may have been left, without a stable partner, to face the daily difficulties of parenting a new-born. Maternal support for the first 8 weeks–10 weeks after delivery should be implemented, with norms established at high political levels. This is especially true for mothers in low-income settings, who may often have limited access to support, especially psychological support, but who are often the most in need of relief.115,116

When comparing the reasons for MMF with those for EFF, many studies also report perceived breast milk insufficiency, BF difficulties, and/or lack of BF confidence to be key drivers to stopping BF.28,117–119 In contrast, the reasons underlying mothers’ decisions to practice FF are often more related to “convenience,” as it is an easy, quick, and “more comfortable” (ie, less embarrassing) way to feed an infant.28,120–122 What distinguishes the drivers of MMF from the drivers of EFF and EBF is the perceived benefits of continued BF while FF, or of introducing FF in addition to BF. Eg, Cabieses et al found that maternal intentions to practice MMF were based on the perceived benefits of combining BF and FF: “… for example, health aspects of BF, with convenience aspects of bottle-feeding ….”28 While some mothers practice MMF due to the perceived health aspects of both breast milk and formula,28,43,100,101 others may have the perception that infant formulas are as nutritious as or even superior to breast milk,30,63,69,81,123 or that supplementation is necessary to achieve an optimal infant weight and health.33,66,84 Again, these discrepancies may be related to a lack of correct information on infant feeding/nutrition or a lack of professional healthcare support.124

Furthermore, there could be a large influence from the misperception that, once FF is introduced, it is impossible to maintain prolonged BF (or even to return to EBF).74 Women feel confused when they receive conflicting messages from the national and international guidelines or healthcare professionals about BF. Indeed, they highlighted the importance of healthcare professionals providing evidence-based and individualized BF advice/information for mothers to reach their BF goals.125 Moreover, healthcare professionals should strive to provide more effective support in helping mothers to succeed in their BF goals and outcomes,126 including when this involves introducing (limited periods of) MMF.

EBF is the best form of nutrition for infants and has several well-documented benefits for both mother and child. At the same time, MMF is a common and widespread practice, due to the reasons described in this review, and it is often implicitly an attempt by a mother to sustain BF rather than switching fully to FF. Some evidence indicates that achieving successful and sustained MMF, with continued BF till weaning, depends partly on the quantity of formula given and the timing of the first supplementation.6,45 MMF indeed decreases a mother’s milk production, since it is a process based on demand127; however, in some cases, MMF can be sustained for several months, for instance if the amount of formula constitutes less than half of the infant’s nutritional intake.6,95,128,129 In a recent study, data from Asia and Europe showed that MMF was sustained for close to 12 months (or possibly longer) in 20% of MMF mums, even when it was introduced relatively soon after birth.6 FF could thus be argued to be a form of extra help—to certain women, in certain cases—for supporting BF for longer, but not as the main source of nutrients.41 Such extra “help” could be physical, but also emotional, depending on the situation. Jacobzon and colleagues (2022) found that MMF mothers felt less stress and pressure knowing that their babies were receiving enough nourishment.10 Similarly, Kossakowska and Bielawska-Batorowicz (2022) observed that MMF appeared to be associated with psychological benefits for mothers.87

Our preliminary findings suggest there may be more likelihood of practicing MMF rather than EBF if income and education levels are slightly lower, and when mothers are employed. These findings require further investigation in future research to establish whether this association does exist, to what extent, and in which populations. Other studies found that medium-to-high income, higher employment, and higher education levels were associated with infant formula supplementation in many countries.6,67,130 Low-income households were associated with higher EBF practices in a Latin American study, except in Colombia, due to overt socioeconomic inequities, and mothers with higher education and the option of formal employment were more likely to practice EBF than mothers with fewer resources.131 Since such data come from observational studies, the reverse causality cannot be excluded, ie, the possibility that MMF was chosen as a method to prolong BF in the case of higher education, more likelihood of formal employment, and higher personal income, vs whether mothers with higher education and greater personal income or employment options are more likely to supplement BF with formula via MMF. In order to further investigate these and other questions, including also the long- and short-term (health) effects of MMF on both mother and child, we also emphasize that a unified definition of MMF is needed.

Our study’s limitations are as follows: MMF remains a difficult topic to reliably research due to intrinsic reasons, lack of randomized controlled trial possibilities, and a high degree of variability in practices and motives. MMF does not describe one feeding behavior, but a collection of heterogeneous feeding behaviors that vary in several aspects across time. No universally recognized definition of MMF exists, and studies often apply arbitrary definitions and categorizations when both BF and FF are given. This may have affected the completeness and accuracy of our findings. We hope that, in the future, informative propensity analyses that come close to models of machine-learning approaches will provide ways of overcoming some of the current research limitations around MMF. The 2 search strategies that were compared here differ slightly in their wording and databases. The search string was improved so it was possible to reach more relevant articles. It was not possible to access one of the databases used in the last systematic review (PsycInfo), and one additional database (Cab Abstracts) was included. These changes brought minimal differences among the results in the search, so this is a limitation. The topic of infant feeding is a sensitive one, and some mothers feel guilty, ashamed, or stigmatized for providing MMF rather than EBF.88,99 Consequently, the reasons they report for providing MMF may be biased toward answers that might be viewed as more favorable or more socially acceptable. In addition, information about the questions asked in the surveys, and questions about the general environment in households creating the specific scenario for choosing an infant feeding method were missing. Nevertheless, these points could be important factors that influence the mothers’ choice and her drivers to practice MMF. The observations on demographic factors associated with MMF are preliminary and descriptive, and do not allow conclusions about the predictors for MMF and their significance. Since reports on MMF demographic characteristics are limited and, when available, studies are observational and cross-sectional in nature, a difference between the MMF and the total sample mean values does not clearly emerge, indicating the need for more precise investigations as primary aims in future studies. Finally, the observational nature of our findings does not allow us a straightforward interpretation of associations, or to disentangle the many inter-related factors at play in parental feeding choices and outcomes.

CONCLUSIONS

Key global drivers for MMF have been identified and described, providing insights and opportunities for the provision of optimal, targeted, BF support. Such support should include strategies for addressing existing maternal insecurities about infant hunger and/or perceived breast milk insufficiencies, particularly in the first weeks after birth, but should also consider the specific setting in which mothers giving MMF live, and their reasons for choosing MMF. A unified definition of MMF is needed to enable more comparable and standardized research. Finally, health and functional outcomes for both MMF mothers and their children should be carefully investigated.

Supplementary Material

nuad134_Supplementary_Data

Acknowledgments

We would like to thank the following people for their assistance in the production of this systematic review: Laura Kaptein acted as a reviewer and revised material for this systematic review. Elif Can led and conducted the search strategy and the initial screening of the articles.

Author contributions. C.M.M., L.F.M., and S.T. designed the research and developed the overall research plan. C.M.M. took a leading role in conducting the research, with contributions from S.T. and support and oversight from L.F.M., P.V., and C.A. S.T. reviewed the articles, edited the manuscript, undertook the data visualization and collection, and carried out the statistical analyses with C.M.M. All authors contributed to the interpretation of the results and the writing of the manuscript. All authors read and approved the final manuscript and take responsibility for its final content.

Funding. The systematic review was funded by Danone Nutricia Research. C.A. was partly supported by a contribution from the Italian Ministry of Health (IRCCS grant).

Declaration of interest. L.F.M. is employed by Danone Nutricia Research, a subsidiary of Danone SA. C.M.M. was hired as a research consultant by Danone Nutricia Research while conducting the systematic review. The other authors have no relevant interests to declare.

Supporting Information

The following Supporting Information is available through the online version of this article at the publisher’s website.

Supplementary methods

Search strategy and selection criteria

Figure S1  MMF drivers mentioned at least once in the earlier systematic review of MMF3

Supplementary results

Table S1  Characteristics of the studies included in this systematic review of MMF3

Table S2  Matrix indicating links between MMF drivers, region, and baby age

QuADS criteria and JBI critical appraisal checklist for systematic reviews, research syntheses, and results of questionnaires

Table S3  QuADS score breakdown by study of the MMF drivers

Table S4  Characteristics of MMF mothers and infants as extracted from the 60 articles containing data on infant age and/or maternal demographic factors associated with MMF

Table S5  Summary of the demographics of MMF, EBF, and the total population of mothers and infants in the present review data

Data Availability

Any extra data underlying this article will be shared on reasonable request to the corresponding author.
==== Refs
REFERENCES

1 Kramer MS , KakumaR.  Optimal duration of exclusive breastfeeding. Cochrane Database Syst Rev.  2012;2012 :CD003517.doi:10.1002/14651858.CD003517.pub2 22895934
2 Neves P , VazJ, MaiaF, et al  Rates and time trends in the consumption of breastmilk, formula, and animal milk by children younger than 2 years from 2000 to 2019: analysis of 113 countries. Lancet Child Adolesc Health.  2021;5 :619–630. doi:10.1016/S2352-4642(21)00163-2 34245677
3 Monge-Montero C , van der MerweLF, PapadimitropoulouK, et al  Mixed milk feeding: a systematic review and meta-analysis of its prevalence and drivers. Nutr Rev.  2020;78 :914–927. doi:10.1093/nutrit/nuaa016 32357372
4 Zakarija-Grković I.  Exclusive breastfeeding in the hospital: how accurate are the data?  J Hum Lact.  2012;28 :139–144. doi:10.1177/0890334412437764 22354468
5 al Sabbah H , AssafEA, TahaZ, et al  Determinants of exclusive breastfeeding and mixed feeding among mothers of infants in Dubai and Sharjah, United Arab Emirates. Front Nutr.  2022;9 :872217.doi:10.3389/fnut.2022.872217 35619950
6 Papadopoulos NG , BalanTA, van der MerweLF, et al  Mixed milk feeding: a new approach to describe feeding patterns in the first year of life based on individual participant data from two randomised controlled trials. Nutrients. 2022;14 :2190.doi:10.3390/nu14112190 35683990
7 Chung SH , KimHR, ChoiYS, et al  Trends of breastfeeding rate in Korea (1994–2012): comparison with OECD and other countries. J Korean Med Sci.  2013;28 :1573–1580. doi:10.3346/jkms.2013.28.11.1573 24265518
8 Lee KS , RhaYH, OhIH, et al  Does breast-feeding relate to development of atopic dermatitis in young Korean children?: based on the fourth and fifth Korea National Health and Nutrition Examination Survey 2007–2012. Allergy Asthma Immunol Res.  2017;9 :307–313. doi:10.4168/aair.2017.9.4.307 28497917
9 McAndrew F , ThompsonJ, FellowsL, et al UK Data Archive Study Number 7281—Infant Feeding Survey. 2010. Available at: https://digital.nhs.uk/data-and-information/publications/statistical/infant-feeding-survey/infant-feeding-survey-uk-2010. Accessed August 4, 2022.
10 Jacobzon A , EngströmÅ, LindbergB, et al  Mothers’ strategies for creating positive breastfeeding experiences: a critical incident study from Northern Sweden. Int Breastfeed J.  2022;17 :35.doi:10.1186/s13006-022-00474-9 35527258
11 Ajetunmobi O , WhyteB, ChalmersJ, et al  Informing the ‘early years‘ agenda in Scotland: understanding infant feeding patterns using linked datasets. J Epidemiol Community Health.  2014;68 :83–92. doi:10.1136/jech-2013-202718 24129609
12 Ruddle L.  Mixed up: Combination Feeding by Choice or Necessity. PRAECLARUS Press; 2021. Available at: https://books.google.nl/books?id=eOtmzgEACAAJ. Accessed August 4, 2022.
13 Jackson L , de PascalisL, HarroldJ, et al  Guilt, shame, and postpartum infant feeding outcomes: a systematic review. Matern Child Nutr.  2021;17 :e13141.doi:10.1111/mcn.13141 33491303
14 The Royal College of Midwives. Infant Feeding. Supporting Parent Choice. 2014. Available at: https://www.rcm.org.uk/media/2355/pressure-points-infant-feeding.pdf. Accessed August 4, 2022.
15 UNICEF United Kingdom. Guide to the Baby Friendly Initiative Standards. Available at: https://www.unicef.org.uk/babyfriendly/baby-friendly-resources/implementing-standards-resources/guide-to-the-standards/. Accessed August 4, 2022.
16 Flaherman VJ , AbyJ, BurgosAE, et al  Effect of early limited formula on duration and exclusivity of breastfeeding in at-risk infants: an RCT. Pediatrics. 2013;131 :1059–1065. doi:10.1542/peds.2012-2809 23669513
17 Moher D , ShamseerL, ClarkeM, et al ; PRISMA-P Group. Preferred reporting items for systematic review and meta-analysis protocols (PRISMA-P) 2015 statement. Syst Rev.  2015;4 :1.doi:10.1186/2046-4053-4-1 25554246
18 Schardt C , AdamsMB, OwensT, et al  Utilization of the PICO framework to improve searching PubMed for clinical questions. BMC Med Inform Decis Mak.  2007;7 :16.doi:10.1186/1472-6947-7-16 17573961
19 Nasser M , van WeelC, van BinsbergenJJ, et al  Generalizability of systematic reviews of the effectiveness of health care interventions to primary health care: concepts, methods and future research. Fam Pract.  2012;29 (suppl 1 ):i94–i103. doi:10.1093/fampra/cmr129 22399564
20 Harrison R , JonesB, GardnerP, et al  Quality Assessment with Diverse Studies (QuADS): an appraisal tool for methodological and reporting quality in systematic reviews of mixed- or multi-method studies. BMC Health Serv Res.  2021;21 :231.doi:10.1186/s12913-021-06122-y 33722212
21 Aromataris E , FernandezR, GodfreyCM, et al  Summarizing systematic reviews: methodological development, conduct and reporting of an umbrella review approach. Int J Evid Based Healthc. 2015;13 :132–140. doi:10.1097/XEB.0000000000000055 26360830
22 Zhu X , TianJ, ChenGL, et al  Predictors of breastfeeding exclusivity in three cities of China. Breastfeed Med.  2014;9 :103–104. doi:10.1089/bfm.2013.0053 24279312
23 Zhao Y , OuyangYQ, ReddingSR.  Attitudes of Chinese adults to breastfeeding in public: a web-based survey. Breastfeed Med.  2017;12 :316–321. doi:10.1089/bfm.2017.0013 28440676
24 Peacock-Chambers E , DicksK, SarathyL, et al  Perceived maternal behavioral control, infant behavior, and milk supply: a qualitative study. J Dev Behav Pediatr.  2017;38 :401–408.28570412
25 Obeng CS , LarsonE.  Parents’ motivations and views on combining breast milk and formula. Int J Child Health Hum Dev. 2014;7 :31–35.
26 Lundberg PC , Ngoc ThuTT.  Breast-feeding attitudes and practices among Vietnamese mothers in Ho Chi Minh City. Midwifery. 2012;28 :252–257. doi:10.1016/j.midw.2011.02.012 21458893
27 Lampl M , MummertA, SchoenM.  Promoting healthy growth or feeding obesity? The need for evidence-based oversight of infant nutritional supplement claims. Healthcare  2016;4 :84.doi:10.3390/healthcare4040084
28 Cabieses B , WaiblingerD, SantorelliG, et al  What factors explain pregnant women’s feeding intentions in Bradford, England: a multi-methods, multi-ethnic study. BMC Pregnancy Childbirth. 2014;14 :50. doi:10.1186/1471-2393-14-50 24472414
29 Alianmoghaddam N , PhibbsS, BennC.  Resistance to breastfeeding: a Foucauldian analysis of breastfeeding support from health professionals. Women Birth.  2017;30 :e281–e291. doi:10.1016/j.wombi.2017.05.005 28648583
30 Jiang H , LiM, YangD, et al  Awareness, intention, and needs regarding breastfeeding: findings from first-time mothers in Shanghai, China. Breastfeed Med.  2012;7 :526–534. doi:10.1089/bfm.2011.0124 22424469
31 Chang S-m , RoweJ, GoopyS.  Non-family support for breastfeeding maintenance among career women in Taiwan: a qualitative study. Int J Nurs Pract.  2014;20 :293–301. doi:10.1111/ijn.12148 24889002
32 Brown A , ShenkerN.  Experiences of breastfeeding during COVID-19: lessons for future practical and emotional support. Matern Child Nutr.  2021;17 :e13088.doi:10.1111/mcn.13088 32969184
33 Glassman ME , McKearneyK, SaslawM, et al  Impact of breastfeeding self-efficacy and sociocultural factors on early breastfeeding in an urban, predominantly Dominican community. Breastfeed Med.  2014;9 :301–307. doi:10.1089/bfm.2014.0015 24902047
34 Hendrick CE , PotterJE.  Nativity, country of education, and Mexican-origin women’s breastfeeding behaviors in the first 10 months postpartum. Birth.  2017;44 :68–77. doi:10.1111/birt.12261 27779318
35 Monroe M , LinaresAM, AshfordK.  Women’s perceptions of hospital-based breastfeeding care and the association with exclusive breastfeeding. Nurs Womens Health.  2021;25 :257–263. doi:10.1016/j.nwh.2021.05.008 34181912
36 Abdul Jafar NK , ThamEKH, PangWW, et al  Association between breastfeeding and sleep patterns in infants and preschool children. Am J Clin Nutr.  2021;114 :1986–1996. doi:10.1093/ajcn/nqab297 34582549
37 Lee S , BaiYK, YouS. B.  Ecological factors influencing breastfeeding decisions among Korean immigrant mothers in America. J Child Fam Stud.  2018;27 :928–943. doi:10.1007/s10826-017-0927-x
38 Xiao X , LokeAY, ZhuS. n, et al  “The sweet and the bitter”: mothers’ experiences of breastfeeding in the early postpartum period: a qualitative exploratory study in China. Int Breastfeed J.  2020;15 :12.doi:10.1186/s13006-020-00256-1 32093764
39 Felice JP , GeraghtySR, QuaglieriCW, et al  “Breastfeeding” but not at the breast: mothers’ descriptions of providing pumped human milk to their infants via other containers and caregivers. Matern Child Nutr. 2017;13 :3–8. doi:10.1111/mcn.12425 28032479
40 al Shahrani A , HushanH, BinjamaanN, et al  Factors associated with early cessation of exclusive breast feeding among Saudi mothers: a prospective observational study. J Family Med Prim Care.  2021;10 :3657–3663. doi:10.4103/jfmpc.jfmpc_852_21 34934662
41 Williamson I , LeemingD, LyttleS, et al  “It should be the most natural thing in the world”: exploring first-time mothers’ breastfeeding difficulties in the UK using audio-diaries and interviews. Matern Child Nutr.  2012;8 :434–447. doi:10.1111/j.1740-8709.2011.00328.x 21696542
42 Annagür A , AnnagürBB, ŞahinAI, et al  Is maternal depressive symptomatology effective on success of exclusive breastfeeding during postpartum 6 weeks?  Breastfeed Med.  2013;8 :53–57. doi:10.1089/bfm.2012.0036 23039400
43 Barcelona De Mendoza V , HarvilleE, TheallK, et al  Acculturation and intention to breastfeed among a population of predominantly Puerto Rican women. Birth. 2016;43 :78–85. doi:10.1111/birt.12199 26554873
44 Bentley JP , NassarN, PorterM, et al  Formula supplementation in hospital and subsequent feeding at discharge among women who intended to exclusively breastfeed: an administrative data retrospective cohort study. Birth.  2017;44 :352–362. doi:10.1111/birt.12300 28737234
45 Whipps MDM , YoshikawaH, DemirciJR, et al  “Painful, yet beautiful, moments”: pathways through infant feeding and dynamic conceptions of breastfeeding success. Qual Health Res.  2022;32 :31–47. doi:10.1177/10497323211032158 34558371
46 Ćwiek D , PrzeradzkaK, StaniszM, et al  Analysis of the impact of selected hospital practices on exclusive breastfeeding . Pomeranian J Life Sci.  2016;62 :25–29. doi:10.21164/pomjlifesci.264
47 Damota K , BañuelosJ, GoldbronnJ, et al  Maternal request for in-hospital supplementation of healthy breastfed infants among low-income women. J Hum Lact.  2012;28 :476–482. doi:10.1177/0890334412445299 22628291
48 Demirtas B.  Breastfeeding support received by Turkish first-time mothers. Int Nurs Rev. 2012;59 :338–344. doi:10.1111/j.1466-7657.2012.00977.x 22897184
49 Hemmingway A , FisherD, BerkeryT, et al  A detailed exploration of early infant milk feeding in a prospective birth cohort study in Ireland: combination feeding of breast milk and infant formula and early breast-feeding cessation. Br J Nutr.  2020;124 :440–449. doi:10.1017/S0007114520001324 32284077
50 Johansson M , FenwickJ, Thies-LagergrenL.  Mothers’ experiences of pain during breastfeeding in the early postnatal period: a short report in a Swedish context. Am J Hum Biol.  2020;32 :e23363.doi:10.1002/ajhb.23363 31800150
51 Koskinen KS , AhoAL, HannulaL, et al  Maternity hospital practices and breast feeding self-efficacy in Finnish primiparous and multiparous women during the immediate postpartum period. Midwifery. 2014;30 :464–470. doi:10.1016/j.midw.2013.05.003 23768951
52 Królak-Olejnik B , BłasiakI, SzczygiełA.  Promotion of breastfeeding in Poland: the current situation. J Int Med Res.  2017;45 :1976–1984. doi:10.1177/0300060517720318 29082794
53 Linares AM , RayensMK, DozierA, et al  Factors influencing exclusive breastfeeding at 4 months postpartum in a sample of urban Hispanic mothers in Kentucky. J Hum Lact.  2015;31 :307–314. doi:10.1177/0890334414565711 25596411
54 Nelson JM , PerrineCG, ScanlonKS, et al  Provision of non-breast milk supplements to healthy breastfed newborns in U.S. hospitals, 2009 to 2013. Matern Child Health J.  2016;20 :2228–2232. doi:10.1007/s10995-016-2095-9 27439419
55 Oniwon O , TenderJAF, HeJ, et al  Reasons for infant feeding decisions in low-income families in Washington, DC. J Hum Lact.  2016;32 :704–710. doi:10.1177/0890334416653739 27389999
56 Rothstein JD , WinchPJ, PachasJ, et al  Vulnerable families and costly formula: a qualitative exploration of infant formula purchasing among peri-urban Peruvian households. Int Breastfeed J.  2021;16 :11.doi:10.1186/s13006-021-00356-6 33468169
57 Misita D , YamamotoJM, YuanY, et al  An exploration of differences in infant feeding practices among women with and without diabetes in pregnancy: a mixed-methods study. Diabet Med.  2021;38 :e14635.doi:10.1111/dme.14635 34265117
58 Boban M , Zakarija-GrkovićI.  In-hospital formula supplementation of healthy newborns: practices, reasons, and their medical justification. Breastfeed Med.  2016;11 :448–454. doi:10.1089/bfm.2016.0039 27548367
59 Chantry CJ , DeweyKG, PeersonJM, et al  In-hospital formula use increases early breastfeeding cessation among first-time mothers intending to exclusively breastfeed. J Pediatr. 2014;164 :1339–1345.e5. doi:10.1016/j.jpeds.2013.12.035 24529621
60 Lewkowitz AK , RaghuramanN, LópezJD, et al  Infant feeding practices and perceived optimal breastfeeding interventions among low-income women delivering at a baby-friendly hospital. Am J Perinatol. 2019;36 :669–677. doi:10.1055/s-0038-1676485 30567004
61 Tawfik S , SaiedD, MostafaO, et al  Formula feeding and associated factors among a group of Egyptian mothers. Open Access Maced J Med Sci.  2019;7 :1854–1859. doi:10.3889/oamjms.2019.462 31316673
62 Bookhart LH , JoynerAB, LeeK, et al  Moving beyond breastfeeding initiation: a qualitative study unpacking factors that influence infant feeding at hospital discharge among urban, socioeconomically disadvantaged women. J Acad Nutr Diet.  2021;121 :1704–1720. doi:10.1016/j.jand.2021.02.005 33715976
63 Gao H , WangQ, HormannE, et al  Breastfeeding practices on postnatal wards in urban and rural areas of the Deyang region, Sichuan province of China. Int Breastfeed J.  2016;11 :11.doi:10.1186/s13006-016-0070-0 27182280
64 Hardison-Moody A , MacNellL, ElliottS, et al  How social, cultural, and economic environments shape infant feeding for low-income women: a qualitative study in North Carolina. J Acad Nutr Diet.  2018;118 :1886–1894.e1. doi:10.1016/j.jand.2018.01.008 29655656
65 Hawley NL , RosenRK, StraitEA, et al  Mothers’ attitudes and beliefs about infant feeding highlight barriers to exclusive breastfeeding in American Samoa. Women Birth.  2015;28 :e80–e86. doi:10.1016/j.wombi.2015.04.002 25935567
66 Safon C , KeeneD, GuevaraWJU, et al  Determinants of perceived insufficient milk among new mothers in León, Nicaragua. Matern Child Nutr. 2017;13 :e12369. doi:10.1111/mcn.12369 27650889
67 Witten C , ClaasenN, KrugerHS, et al  Psychosocial barriers and enablers of exclusive breastfeeding: lived experiences of mothers in low-income townships, North West Province, South Africa. Int Breastfeed J.  2020;15 :76.doi:10.1186/s13006-020-00320-w 32847591
68 Al-shehri H , AlmozaaiR, KaririM, et al  Factors associated with safe infant sleep practices in Saudi Arabia. Pediatric Health Med Ther.  2021;12 :533–541. doi:10.2147/phmt.s343535 34955665
69 Garrett CC , AzimovM, CampwalaK, et al  Breastfeeding practices among Hispanic and non-Hispanic women at the postpartum visit. J Hum Lact.  2018;34 :485–493. doi:10.1177/0890334418774765 29787690
70 Idris FP , KanangB, AdrianiF, et al  Mother’s behavior in breastfeeding in Gowa Regency, South Sulawesi (study on mothers with insufficient breastmilk production). Gac Sanit.  2021;35 (suppl 2 ):S472–S474. doi:10.1016/j.gaceta.2021.06.011 34929878
71 Karall D , NdayisabaJP, HeichlingerA, et al  Breast-feeding duration: early weaning—do we sufficiently consider the risk factors?  J Pediatr Gastroenterol Nutr.  2015;61 :577–582. doi:10.1097/MPG.0000000000000873 26020371
72 Kent JC , AshtonE, HardwickCM, et al  Causes of perception of insufficient milk supply in Western Australian mothers. Matern Child Nutr.  2021;17 :e13080.doi:10.1111/mcn.13080 32954674
73 Kuswara K , CampbellKJ, HeskethKD, et al  Patterns and predictors of exclusive breastfeeding in Chinese Australian mothers: a cross sectional study. Int Breastfeed J.  2020;15 :61.doi:10.1186/s13006-020-00304-w 32660501
74 McCoy MB , HeggieP.  In-hospital formula feeding and breastfeeding duration. Pediatrics. 2020;146 :4. doi:10.1542/peds.2019-2946
75 Mensah KA , AcheampongE, AnokyeFO, et al  Factors influencing the practice of exclusive breastfeeding among nursing mothers in a peri-urban district of Ghana. BMC Res Notes.  2017;10 :466.doi:10.1186/s13104-017-2774-7 28882162
76 Pierro J , AbulaimounB, RothP, et al  Factors associated with supplemental formula feeding of breastfeeding infants during postpartum hospital stay. Breastfeed Med.  2016;11 :196–202. doi:10.1089/bfm.2015.0091 27027901
77 Pinheiro JMF , FlorTBM, GermanoMG, et al  Feeding practices and early weaning in the neonatal period: a cohort study. Rev Saude Publica.  2021;55 :63. doi:10.11606/s1518-8787.2021055003248 34706039
78 Rozensztrauch A , KlaniewskaM, Berghausen-MazurM.  Factors affecting the mother’s choice of infant feeding method in Poland – a cross-sectional preliminary study in Poland. Ir J Med Sci. 2022;191 :1735–1743. doi:10.1007/s11845-021-02751-8
79 Maehara K , MoriE, IwataH, et al  Postpartum maternal function and parenting stress: comparison by feeding methods. Int J Nurs Pract. 2017;23 (suppl 1 ):e12549. doi:10.1111/ijn.12549
80 Hohl S , ThompsonB, EscareñoM, et al  Cultural norms in conflict: breastfeeding among Hispanic immigrants in rural Washington State. Matern Child Health J.  2016;20 :1549–1557. doi:10.1007/s10995-016-1954-8 27021068
81 Radzyminski S , CallisterLC.  Mother’s beliefs, attitudes, and decision making related to infant feeding choices. J Perinat Educ.  2016;25 :18–28. doi:10.1891/1058-1243.25.1.18 26848247
82 al Shahrani A , HushanH, BinjamaanN, et al  Factors associated with early cessation of exclusive breast feeding among Saudi mothers: a prospective observational study. J Family Med Prim Care.  2021;10 :3657–3663. doi:10.4103/jfmpc.jfmpc_852_21 34934662
83 Garrison MP , MaisanoP.  Systematic review of factors influencing non–medically indicated formula supplementation of newborns in the hospital setting. Nurs Womens Health.  2019;23 :340–350. doi:10.1016/j.nwh.2019.06.003 31400848
84 Jones A , RellerL, KnowlesJ, et al  Decisions regarding newborn feeding by Latina mothers. Clin Pediatr (Phila).  2018;57 :168–172. doi:10.1177/0009922817692317 28952343
85 Shepherd L , WalbeyC, LovellB.  The role of social-cognitive and emotional factors on exclusive breastfeeding duration. J Hum Lact.  2017;33 :606–613. doi:10.1177/0890334417708187 28602112
86 Galipeau R , DumasL, LepageM.  Perception of not having enough milk and actual milk production of first-time breastfeeding mothers: is there a difference?  Breastfeed Med.  2017;12 :210–217. doi:10.1089/bfm.2016.0183 28326807
87 Kossakowska K , Bielawska-BatorowiczE.  Postpartum depressive symptoms and their selected psychological predictors in breast-, mixed and formula-feeding mothers. Front Psychiatry.  2022;13 :813469.doi:10.3389/fpsyt.2022.813469 35185655
88 Komninou S , FallonV, HalfordJCG, et al  Differences in the emotional and practical experiences of exclusively breastfeeding and combination feeding mothers. Matern Child Nutr. 2017;13 :e12364.doi:10.1111/mcn.12364 27714927
89 Kent JC , PrimeDK, GarbinCP.  Principles for maintaining or increasing breast milk production. J Obstet Gynecol Neonatal Nurs.  2012;41 :114–121. doi:10.1111/j.1552-6909.2011.01313.x
90 Ventura A.  Chapter 1. Introduction. In: VenturaA, ed. Promoting Responsive Feeding during Breastfeeding, Bottle-Feeding, and the Introduction to Solid Foods. Academic Press; 2022: 1. doi:10.1016/B978-0-323-88452-5.00011-5
91 Chen TL , ChenYY, LinCL, et al  Responsive feeding, infant growth, and postpartum depressive symptoms during 3 months postpartum. Nutrients. 2020;12 :1–14. doi:10.3390/nu12061766
92 Heinig JM , BañuelosJI, GoldbronnJM, et al Fit WIC Baby Behavior Study. Helping You Understand Your Baby. CW Program; 2009.
93 Marshall JL , GodfreyM, RenfrewMJ.  Being a ‘good mother’: managing breastfeeding and merging identities. Soc Sci Med.  2007;65 :2147–2159. doi:10.1016/j.socscimed.2007.06.015 17681409
94 Wood NK , SandersEA, LewisFM, et al  Pilot test of a home-based program to prevent perceived insufficient milk. Women Birth.  2017;30 :472–480. doi:10.1016/j.wombi.2017.04.006 28529088
95 Ibarra-Ortega A , Vásquez-GaribayEM, Larrosa-HaroA, et al  Using a lactation room at the workplace is associated with longer breastfeeding duration in working mothers. Nutr Hosp.  2020;37 :918–925. doi:10.20960/nh.03242 32960635
96 Neves PAR , Gatica-DomínguezG, RollinsNC, et al  Infant formula consumption is positively correlated with wealth, within and between countries: a multi-country study. J Nutr.  2020;150 :910–917. doi:10.1093/jn/nxz327 31875480
97 Kramer MS , ChalmersB, HodnettED, et al ; PROBIT Study Group (Promotion of Breastfeeding Intervention Trial). Promotion of Breastfeeding Intervention Trial (PROBIT): a randomized trial in the Republic of Belarus. JAMA. 2001;285 :413–420. doi:10.1001/jama.285.4.413 11242425
98 Victora CG , BahlR, BarrosAJD, et al ; Lancet Breastfeeding Series Group. Breastfeeding in the 21st century: epidemiology, mechanisms, and lifelong effect. Lancet.  2016;387 :475–490. doi:10.1016/S0140-6736(15)01024-7 26869575
99 Asiodu IV , WatersCM, DaileyDE, et al  Infant feeding decision-making and the influences of social support persons among first-time African American mothers. Matern Child Health J.  2017;21 :863–872. doi:10.1007/s10995-016-2167-x 27565664
100 Cartagena DC , AmeringerSW, McgrathJ, et al  Factors contributing to infant overfeeding with Hispanic mothers. J Obstet Gynecol Neonatal Nurs.  2014;43 :139–159. doi:10.1111/1552-6909.12279
101 Ahluwalia IB , D’AngeloD, MorrowB, et al  Association between acculturation and breastfeeding among Hispanic women: data from the pregnancy risk assessment and monitoring system. J Hum Lact.  2012;28 :167–173. doi:10.1177/0890334412438403 22526345
102 Fischer TP , OlsonBH.  A qualitative study to understand cultural factors affecting a mother’s decision to breast or formula feed. J Hum Lact.  2014;30 :209–216. doi:10.1177/0890334413508338 24186645
103 Henninger ML , IrvingSA, KauffmanTL, et al ; Pregnancy and Influenza Project Workgroup. Predictors of breastfeeding initiation and maintenance in an integrated healthcare setting. J Hum Lact.  2017;33 :256–266. doi:10.1177/0890334417695202 28418800
104 Emmanuel A , ClowS.  Infant feeding intentions of pregnant women in Plateau State, Nigeria. Afr J Nurs Midwifery. 2016;10 :83–89. doi.org/10.12968/ajmw.2016.10.2.83
105 Odom EC , LiR, ScanlonKS, et al  Association of family and health care provider opinion on infant feeding with mother’s breastfeeding decision. J Acad Nutr Diet.  2014;114 :1203–1207. doi:10.1016/j.jand.2013.08.001 24200653
106 Demirtas B.  Breastfeeding support received by Turkish first-time mothers. Int Nurs Rev.  2012;59 :338–344. doi:10.1111/j.1466-7657.2012.00977.x 22897184
107 Whaley SE , MeehanK, LangeL, et al  Predictors of breastfeeding duration for employees of the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). J Am Diet Assoc.  2002;102 :1290–1293. doi:10.1016/S0002-8223(02)90284-1 12792629
108 Butte NF , Lopez-AlarconMG, GarzaC; Expert Consultation on the Optimal Duration of Exclusive Breastfeeding (2001: Geneva, Switzerland). Nutrient adequacy of exclusive breastfeeding for the term infant during the first six months of life. World Health Organization 2002. Available at: https://apps.who.int/iris/handle/10665/42519. Accessed August 4, 2022.
109 Ferguson MC , O’SheaKJ, HammerLD, et al  Can following formula-feeding recommendations still result in infants who are overweight or have obesity?  Pediatr Res.  2020;88 :661–667. doi:10.1038/s41390-020-0844-3 32179869
110 Bloomfield FH , AgostoniC.  The potential impact of feeding formula-fed infants according to published recommendations. Pediatr Res.  2020;88 :526–528. doi:10.1038/s41390-020-1056-6 32634816
111 Piankusol C , SirikulW, OngprasertK, et al  Factors affecting breastfeeding practices under lockdown during the COVID-19 pandemic in Thailand: a cross-sectional survey. Int J Environ Res Public Health. 2021;18 :8729.doi:10.3390/ijerph18168729 34444479
112 Vazquez-Vazquez A , DibS, RougeauxE, et al  The impact of the Covid-19 lockdown on the experiences and feeding practices of new mothers in the UK: preliminary data from the COVID-19 New Mum Study. Appetite. 2021;156 :104985.doi:10.1016/j.appet.2020.104985 33038477
113 Ronchi A , PietrasantaC, ZavattoniM, et al  Evaluation of rooming-in practice for neonates born to mothers with severe acute respiratory syndrome coronavirus 2 infection in Italy. JAMA Pediatr.  2021;175 :260–266. doi:10.1001/jamapediatrics.2020.5086 33284345
114 Zanardo V , TortoraD, GuerriniP, et al  Infant feeding initiation practices in the context of COVID-19 lockdown. Early Hum Dev.  2021;152 :105286.doi:10.1016/j.earlhumdev.2020.105286 33276222
115 Fisher J , Cabral de MelloM, PatelV, et al  Prevalence and determinants of common perinatal mental disorders in women in low- and lower-middle-income countries: a systematic review. Bull World Health Organ.  2012;90 :139G–149G. doi:10.2471/BLT.11.091850
116 Saxena S , ThornicroftG, KnappM, et al  Resources for mental health: scarcity, inequity, and inefficiency. Lancet.  2007;370 :878–889. doi:10.1016/S0140-6736(07)61239-2 17804062
117 Alfaleh K , AlosaimiA, AljefriS, et al  Infant formula in Saudi Arabia: a cross sectional survey. J Kuwait Medical Assoc. 2014;46 :328–332. Available at: https://www.researchgate.net/publication/267393168. Accessed August 4, 2022.
118 al Juaid DAM , BinnsCW, GigliaRC.  Breastfeeding in Saudi Arabia: a review. 2014;9 :1. doi: 10.1186/1746-4358-9-1
119 Tawfik S , SaiedD, MostafaO, et al  Formula feeding and associated factors among a group of Egyptian mothers. Open Access Maced J Med Sci.  2019;7 :1854–1859. doi:10.3889/oamjms.2019.462 31316673
120 Tarrant RC , Sheridan-PereiraM, McCarthyRA, et al  Mothers who formula feed: their practices, support needs and factors influencing their infant feeding decision. Child Care in Practice. 2013;19 :78–94. doi:10.1080/13575279.2012.737764
121 Brown A , RaynorP, LeeM.  Healthcare professionals’ and mothers’ perceptions of factors that influence decisions to breastfeed or formula feed infants: a comparative study. J Adv Nurs.  2011;67 :1993–2003. doi:10.1111/j.1365-2648.2011.05647.x 21507050
122 Bonia K , TwellsL, HalfyardB, et al  A qualitative study exploring factors associated with mothers’ decisions to formula-feed their infants in Newfoundland and Labrador, Canada. BMC Public Health.  2013;13 :645.doi:10.1186/1471-2458-13-645 23844590
123 Mitiku A.  Formula feeding and associated factors among mothers with infants 0–6 months old in Mettu Town, South West Ethiopia. Food Sci Nutr. 2023;11 :4136–4145. doi:10.21203/rs.3.rs-965060/v1 37457147
124 Nyaloko MJ.  Perceptions of Mothers and Community Members Regarding Breastfeeding in Public Spaces of Urban Gauteng in South Africa [dissertation]. Potchefstroom: North-West University (South Africa); 2020.
125 Blixt I , JohanssonM, HildingssonI, et al  Women’s advice to healthcare professionals regarding breastfeeding: “offer sensitive individualized breastfeeding support”- an interview study. Int Breastfeed J.  2019;14 :51.doi:10.1186/s13006-019-0247-4 31889974
126 McFadden A , GavineA, RenfrewMJ, et al  Support for healthy breastfeeding mothers with healthy term babies. Cochrane Database Syst Rev.  2017;2 :CD001141. doi:10.1002/14651858.CD001141.pub5 28244064
127 Daly SEJ , HartmannPE.  Infant demand and milk supply. Part 1: infant demand and milk production in lactating women. J Hum Lact.  1995;11 :21–26. doi:10.1177/089033449501100119 7718102
128 Kay MC , CholeraR, FlowerKB, et al  Are low-income, diverse mothers able to meet breastfeeding intentions after 2 months of breastfeeding?  Breastfeed Med.  2020;15 :435–442. doi:10.1089/bfm.2020.0025 32357088
129 Yorifuji T , KuboT, YamakawaM, et al  Breastfeeding and behavioral development: a nationwide longitudinal survey in Japan. J Pediatr. 2014;164 :1019–1025.e3. doi:10.1016/j.jpeds.2014.01.012 24529622
130 Maharlouei N , PourhaghighiA, Raeisi ShahrakiH, et al  Factors affecting exclusive breastfeeding, using adaptive LASSO regression. Int J Community Based Nurs Midwifery. 2018;6 :260–271.30035142
131 Ferreira CS , AzeredoCM, RinaldiAEM.  Trends in social inequalities in breastfeeding and infant formulas in Latin American countries between the 1990 and 2010 decades. Public Health Nutr.  2021;24 :5471–5480. doi:10.1017/S1368980021000392 33500006
