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Factors associated with exclusive breastfeeding in the first six months of life in Brazil: a systematic review

ABSTRACT

OBJECTIVE

To identify factors associated with exclusive breastfeeding in the first six months of life in Brazil.

METHODS

Systematic review of epidemiological studies conducted in Brazil with exclusive breastfeeding as outcome. Medline and LILACS databases were used. After the selection of articles, a hierarchical theoretical model was proposed according to the proximity of the variable to the outcome.

RESULTS

Of the 67 articles identified, we selected 20 cross-sectional studies and seven cohort studies, conducted between 1998 and 2010, comprising 77,866 children. We identified 36 factors associated with exclusive breastfeeding, being more often associated the distal factors: place of residence, maternal age and education, and the proximal factors: maternal labor, age of the child, use of a pacifier, and financing of primary health care.

CONCLUSIONS

The theoretical model developed may contribute to future research, and factors associated with exclusive breastfeeding may subsidize public policies on health and nutrition.

Breast Feeding; Maternal Behavior; Risk Factors; Socioeconomic Factors; Review

RESUMO

OBJETIVO

Identificar fatores associados ao aleitamento materno exclusivo nos primeiros seis meses de vida no Brasil.

MÉTODOS

Revisão sistemática de estudos epidemiológicos conduzidos no Brasil com o aleitamento materno exclusivo como desfecho. Foram utilizadas as bases de dados Medline e Lilacs. Após a seleção de artigos, foi proposto um modelo teórico hierarquizado, segundo a proximidade da variável com o desfecho.

RESULTADOS

Dos 67 artigos identificados, foram selecionados 20 estudos transversais e sete de coorte, conduzidos entre 1998 e 2010, compreendendo 77.866 crianças. Foram identificados 36 fatores associados ao aleitamento materno exclusivo, sendo mais frequentemente associados os fatores distais: local de residência, idade e escolaridade maternas, e os fatores proximais: trabalho materno, idade da criança, uso de chupeta e financiamento da atenção primária em saúde.

CONCLUSÕES

O modelo teórico desenvolvido pode contribuir para a condução de futuras pesquisas e os fatores associados ao aleitamento materno exclusivo podem subsidiar políticas públicas em saúde e nutrição.

Aleitamento Materno; Comportamento Materno; Fatores de Risco; Fatores Socioeconômicos; Revisão

INTRODUCTION

Breastfeeding is a crucial issue for public health, for it directly affects the standards of health and mortality of populations.44. Boccolini CS, Carvalho ML, Oliveira MI, Boccolini PM. O papel do aleitamento materno na redução das hospitalizações por pneumonia em crianças brasileiras menores de 1 ano. J Pediatr (Rio J). 2011;87(5):399-404. DOI:10.2223/JPED.2136,1414. Escuder MML, Venâncio SI, Pereira JCR. Estimativa de impacto da amamentação sobre a mortalidade infantil. Rev Saude Publica. 2003;37(3):319-25. DOI:10.1590/S0034-89102003000300009,2020. Kramer MS, Kakuma R. The optimal duration of exclusive breastfeeding: a systematic review. Adv Exp Med Biol. 2004;554:63-77. DOI:10.1007/978-1-4757-4242-8_7,3939. Roth DE, Caulfield LE, Ezzat M, Black RE. Acute lower respiratory infections in childhood: opportunities for reducing the global burden through nutritional interventions. Bull World Health Organ. 2008;86(5):356-64. DOI:10.2471/BLT.07.049114,5353. WHO Collaborative Study Team on the Role of Breastfeeding on the Prevention of Infant Mortality. Effect of breastfeeding on infant and child mortality due to infectious diseases in less developed countries: a pooled analysis. Lancet. 2000;355(9202):451-5. DOI:10.1016/S0140-6736(00)82011-5 The prevalence and duration of partial or exclusive breastfeeding increased in all social strata and regions of Brazil between the decades of 1990 and 2010.35,45,a a Ministério da Saúde, Secretaria de Atenção à Saúde, Departamento de Ações Programáticas e Estratégicas. II Pesquisa de prevalência de aleitamento materno nas capitais brasileiras e Distrito Federal. Brasília (DF): Ministério da Saúde; 2009. (Série C. Projetos, programas e relatórios). ,b b Ministério da Saúde. PNDS 2006: pesquisa nacional de demografia e saúde da criança e da mulher. Brasília (DF): Ministério da Saúde; 2008. Part of this trend can be attributed to national policies of breastfeeding promotion, protection, and support.3535. Rea MF. Reflexões sobre a amamentação no Brasil: de como passamos a 10 meses de duração. Cad Saude Publica. 2003;19(Supl 1):S37-45. DOI:10.1590/S0102-311X2003000700005

Different social and cultural contexts may influence the practice of exclusive breastfeeding and its determinants. A study conducted in cities of three countries noted that higher levels of maternal education were related both with higher prevalence of exclusive breastfeeding in Santos, SP, Southeastern Brazil, and with lower prevalence in Mexico City, Mexico, and in Sula and Tegucigalpa, Honduras.3232. Pérez-Escamilla R, Lutter C, Segall AM, Rivera A, Treviño-Siller S, Sanghvi T. Exclusive breast-feeding duration is associated with attitudinal, socioeconomic and biocultural determinants in three Latin American countries. J Nutr. 1995;125(12):2972-84.

Seeking greater population homogeneity, this review was restricted to the Brazilian context, since the determinants of exclusive breastfeeding may behave differently in diverse cultures.

The aim of this study was to identify the factors associated with exclusive breastfeeding in the first six months of life in Brazil.

METHODS

Publications of epidemiological studies conducted in Brazil about factors associated with exclusive breastfeeding were analized. Bibliographical research was carried out on Medline (via PubMed) and LILACS databases. Delimitation by period or by language were not considered. A manual search of the references included in the bibliography of each article was carried out.

The searches were independently conducted in July 2014 by two reviewers. The advanced search terms for the PubMed were: (exclusive[All Fields] AND ("breast feeding" [MeSH Terms] OR ("breast"[All Fields] AND "feeding"[All Fields]) OR "breast feeding"[All Fields] OR "breastfeeding"[All Fields]) AND ("Brazil"[MeSH Terms] OR "Brazil"[All Fields])) AND (determinants[All Fields] OR factors[All Fields] OR ("epidemiology"[Subheading] OR "epidemiology"[All Fields] OR "epidemiology"[MeSH Terms]))".

In the LILACS database were searched, in the "search details", the following terms: "tw:(tw: (exclusive AND breastfeeding (epidemiology OR determinants OR factors)) AND (instance:"regional") AND (db:("LILACS"))) AND (instance:"regional") AND (mj:("Breastfeeding"))". The terms were also used in Portuguese: "tw:(aleitamento AND materno AND exclusivo) AND (instance:"regional") AND (db:("LILACS") AND mj:("Aleitamento materno")) OR fatores)) AND (instance:"regional") AND (db:("LILACS"))". The term "Brazil" was not employed in this database, since it has only articles published in journals of Latin America and Caribbean.

Observational analytical epidemiological studies were included, in which exclusive breastfeeding was treated as outcome, with adjustment of the factors studied together and for possible confounding factors, which have adopted the definition of the World Health Organization (WHO)c c World Health Organization. Indicators for assessing infant and young child feeding practices. Part 1: definitions. Conclusions of a consensus meeting held 6-8 November 2007 in Washington, DC, USA. Geneva: World Health Organization; 2007. for exclusive breastfeeding (children receive only human milk, directly from their mother or extracted, and no longer receive any other liquid or solid, except vitamin drops or syrups, vitamin supplements or medication) and whose sampling procedure has generated a representative population of infants from maternities, cities, states, or of the Brazilian nation.

In articles which more than one age group was evaluated (more than a statistical model to evaluate two or more different age groups), the age group of older age was chosen (with a limit of six months), since the objective was to evaluate the outcome closer to the WHOc c World Health Organization. Indicators for assessing infant and young child feeding practices. Part 1: definitions. Conclusions of a consensus meeting held 6-8 November 2007 in Washington, DC, USA. Geneva: World Health Organization; 2007. recommendation of exclusive breastfeeding until six months of age.

The following studies were excluded: those with results subject to selection bias (such as losses exceeding 20.0%) or with possible information bias (such as interviews with mothers of children over one year old); that presented only the p value (without presenting the association measures), which considered only the population born with low weight; and bibliographic reviews (systematic or unsystematic).

In the case of studies using the same database and published in more than one article (different journals and years), we included those that used different age groups or different analytical variables and methods.

The selected articles were stored under the Portable Document Format (PDF) into a directory shared in the cloud, separated according to databases of origin (Medline and LILACS), and classified into different folders between included and excluded.

The evaluation of the methodological quality of the selected studies was obtained by adjusting the scale "Effective Public Health Practice Project: Quality Assessment Tool for Quantitative Studies – QATQS" (http://www.ephpp.ca/tools.html). Of this scale, five questions were evaluated (classified as "strong", "moderate", or "weak"): 1) selection bias; 2) study design; 3) confounding factors; 4) data collection methods; and 5) type of analysis employed for the outcome. Blinding issues of QATQS were not used in any study (since no clinical trial was included), and issues of loss of follow-up were not applied in sectional studies. In the "study design" question, sectional studies had lower score than the cohort studies, because in sectional studies the temporality between exposition variables and the outcome may not always be established.

Considering the final score of the QATQS scale of each article selected, the articles were considered strong if none of the questions were rated as weak; moderate, in the case of studies that showed one of the questions rated as weak; and weak, studies with one or more questions thus evaluated.

Data extraction was independently performed by two reviewers by a structured form, in which were recorded: the last name of the first author; publishing journal and year; location(s) of performance; year and period of performance; study design; population of the study; sample design used; strategy for selection of subjects of research; inclusion and exclusion criteria; total sample number; sample number evaluated; total losses and reason of losses; age group of the studied children; type of outcome; type of statistical analysis; factors of control or adjusting the statistical model; results of the model with association measure and statistical significance; exclusive breastfeeding prevalence or median; limitations of the study; and observations. In the event of disagreement among peers, a third reviewer was consulted.

Data tabulation included: reference of the article (with the last name of the first author, journal, and year of publication); location of the study and data collection; sample number evaluated (and data source); outcome of the study (exclusive breastfeeding or its interruption); statistical analysis employed; prevalence (or median) of exclusive breastfeeding found and the age group of this prevalence (expressed in months); factors associated with exclusive breastfeeding in a statistically significant manner (obtained from the results of the statistical models), as well as its association measure and other factors evaluated without statistically significant association with exclusive breastfeeding.

Two tables were made, one for cross-sectional studies and another for cohort studies. As the revised studies measured the prevalence or the duration of exclusive breastfeeding in different age groups, the summary tables of this outcome contain this information.

The next step consisted in individually analyzing the association found between the factors investigated and exclusive breastfeeding, highlighting and quantifying the following aspects: in how many studies these factors were investigated, in how many studies an association with exclusive breastfeeding was identified in statistical models and what is its direction.

The last step of the study consisted in creating a hierarchical theoretical model (using the assumptions established by Víctora et al)4949. Victora CG, Huttly SR, Fuchs SC, Olinto MTA. The role of conceptual frameworks in epidemiological analysis: a hierarchical approach. Int J Epidemiol. 1997;26(1):224-7. DOI:10.1093/ije/26.1.224 organizing all factors found according to the proximity to the outcome. The selection of the allocation levels of variables followed the logic of chronological classification between factors present before pregnancy, during pregnancy, immediate postpartum and at the time of discharge until six months of life.

Four levels of variables were proposed, grouped in hierarchical blocks: 1) distal characteristics (contextual, domestic, household, and maternal); 2) distal intermediate (from pregnancy and prenatal care); 3) proximal intermediate (childbirth care, maternal characteristics during hospitalization, and characteristics of the newborn); 4) proximal (characteristics of the nursing mothers and the family, of the babies, and of health services).

To provide parsimony to the summary of variables identified and also for the creation of the theoretical model, the terminology used in each article for each variable was standardized.

RESULTS

Of the 67 articles retrieved by electronic search, 44 were excluded because they did not meet the selection criteria. After manual search, four articles were included,2121. Leone CR, Sadeck LSR. Fatores de risco associados ao desmame em crianças até seis meses de idade no município de São Paulo. Rev Paul Pediatr. 2012;30(1):21-6. DOI:10.1590/S0103-05822012000100004,2929. Neves ACM, Moura EC, Santos W, Carvalho KMB. Factors associated with exclusive breastfeeding in the Legal Amazon and Northeast regions, Brazil, 2010. Rev Nutr. 2014;27(1):81-95. DOI:10.1590/1415-52732014000100008,3838. Rito RVVF, Oliveira MIC, Brito AS. Grau de cumprimento dos Dez Passos da Iniciativa Unidade Básica Amiga da Amamentação e sua associação com a prevalência de aleitamento materno exclusivo. J Pediatr (Rio J). 2013;89(5):477-84. DOI:10.1016/j.jped.2013.02.018,4444. Vannuchi MTO, Thomson Z, Escuder MML, Tacia MTGM, Venozzo KMK, Castro LMCP, Oliveira MBM, Venancio SI. Perfil do aleitamento materno em menores de um ano no Município de Londrina, Paraná. Rev Bras Saude Mater Infant. 2005;5(2):155-62. DOI:10.1590/S1519-38292005000200003 totaling 27 articles selected for the analysis55. Bueno MB, Souza JM, Souza SB, Paz SM, Gimeno SG, Siqueira AA. Riscos associados ao processo de desmame entre crianças nascidas em hospital universitário de São Paulo, entre 1998 e 1999: estudo de coorte prospectivo do primeiro ano de vida. Cad Saude Publica. 2003;19(5):1453-60. DOI:10.1590/S0102-311X2003000500024

6. Caminha MF, Batista Filho M, Serva VB, Arruda IKG, Figueiroa JN, Lira PIC. Tendências temporais e fatores associados à duração do aleitamento materno em Pernambuco. Rev Saude Publica. 2010;44(2):240-8. DOI:10.1590/S0034-89102010000200003
-77. Carvalhaes MABL, Parada CMGL, Costa MP. Fatores associados à situação do aleitamento materno exclusivo em crianças menores de 4 meses, em Botucatu - SP. Rev Lat Am Enfermagem. 2007;15(1):62-9. DOI:10.1590/S0104-11692007000100010,99. Chaves RG, Lamounier JA, César CC. Fatores associados com a duração do aleitamento materno. J Pediatr (Rio J.). 2007;83(3):241-6. DOI:10.1590/S0021-75572007000400009

10. Damião JJ. Influência da escolaridade e do trabalho maternos no aleitamento materno exclusivo. Rev Bras Epidemiol. 2008;11(3):442-52. DOI:10.1590/S1415-790X200800030001
-1111. Demétrio F, Pinto EJ, Assis AMO. Fatores associados à interrupção precoce do aleitamento materno: um estudo de coorte de nascimento em dois municípios do Recôncavo da Bahia, Brasil. Cad Saude Publica. 2012;28(4):641-54. DOI:10.1590/S0102-311X2012000400004,1515. Fernandes TA, Werneck GL, Hasselmann MH. Prepregnancy weight, weight gain during pregnancy, and exclusive breastfeeding in the first month of Life in Rio de Janeiro, Brazil. J Hum Lact. 2012;28(1):55-61. DOI:10.1177/0890334411429113,1616. França GVA, Brunken GS, Silva SM, Escuder MM, Venancio SI. Determinantes da amamentação no primeiro ano de vida em Cuiabá, Mato Grosso. Rev Saude Publica. 2007;41(5):711-8. DOI:10.1590/S0034-89102007000500004,1818. Gusmão AM, Béria JU, Gigante LP, Leal AF, Schermann LB. Prevalência de aleitamento materno exclusivo e fatores associados: estudo transversal com mães adolescentes de 14 a 16 anos em Porto Alegre, RS, Brasil. Cien Saude Colet. 2013;18(11):3357-68. DOI:10.1590/S1413-81232013001100025,2121. Leone CR, Sadeck LSR. Fatores de risco associados ao desmame em crianças até seis meses de idade no município de São Paulo. Rev Paul Pediatr. 2012;30(1):21-6. DOI:10.1590/S0103-05822012000100004,2323. Martins CC, Vieira GO, Vieira TO, Mendes CM. Fatores de riscos maternos e de assistência ao parto para interrupção precoce do aleitamento materno exclusivo: estudo de coorte. Rev Baiana Saude Publica. 2011;35(Supl 1):167-8.,2424. Mascarenhas MLW, Albernaz EP, Silva MB, Silveira RB. Prevalência de aleitamento materno exclusivo nos 3 primeiros meses de vida e seus determinantes no Sul do Brasil. J Pediatr (Rio J.). 2006;82(4):289-94. DOI:10.1590/S0021-75572006000500011,2828. Nascimento MBR, Reis MAM, Franco SC, Issler H, Ferraro AA, Grisi SJFE. Exclusive breastfeeding in southern Brazil: prevalence and associated factors. Breastfeed Med. 2010;5(2):79-85. DOI:10.1089/bfm.2009.0008

29. Neves ACM, Moura EC, Santos W, Carvalho KMB. Factors associated with exclusive breastfeeding in the Legal Amazon and Northeast regions, Brazil, 2010. Rev Nutr. 2014;27(1):81-95. DOI:10.1590/1415-52732014000100008

30. Parizoto GM, Parada CMGL, Venâncio SI, Carvalhaes MABL. Tendência e determinantes do aleitamento materno exclusivo em crianças menores de 6 meses. J Pediatr (Rio J.). 2009;85(3):201-8. DOI:10.1590/S0021-75572009000300004
-3131. Pereira RSV, Oliveira MIC, Andrade CLT, Brito AS. Fatores associados ao aleitamento materno exclusivo: o papel do cuidado na atenção básica. Cad Saude Publica.2010;26(12):2343-54. DOI:10.1590/S0102-311X2010001200013,3434. Queluz MC, Pereira MJB, Santos CB, Leite AM, Ricco RG. Prevalência e determinantes do aleitamento materno exclusivo no município de Serrana, São Paulo, Brasil. Rev Esc Enferm USP. 2012;46(3):537-43. DOI:10.1590/S0080-62342012000300002,3939. Roth DE, Caulfield LE, Ezzat M, Black RE. Acute lower respiratory infections in childhood: opportunities for reducing the global burden through nutritional interventions. Bull World Health Organ. 2008;86(5):356-64. DOI:10.2471/BLT.07.049114,4040. Santo LC, Oliveira LD, Giugliani ER. Factors associated with low incidence of exclusive breastfeeding for the first 6 months. Birth. 2007;34(3):212-9. DOI:10.1111/j.1523-536X.2007.00173.x,4343. Silva MB, Albernaz EP, Mascarenhas MLW, Silveira RB. Influência do apoio à amamentação sobre o aleitamento materno exclusivo dos bebês no primeiro mês de vida e nascidos na cidade de Pelotas, Rio Grande do Sul, Brasil. Rev Bras Saude Mater Infant. 2008;8(3):275-84. DOI:10.1590/S1519-38292008000300006

44. Vannuchi MTO, Thomson Z, Escuder MML, Tacia MTGM, Venozzo KMK, Castro LMCP, Oliveira MBM, Venancio SI. Perfil do aleitamento materno em menores de um ano no Município de Londrina, Paraná. Rev Bras Saude Mater Infant. 2005;5(2):155-62. DOI:10.1590/S1519-38292005000200003

45. Venancio SI, Monteiro CA. A tendência da prática da amamentação no Brasil nas décadas de 70 e 80. Rev Bras Epidemiol. 1998;1(1):40-9. DOI:10.1590/S1415-790X1998000100005

46. Venancio SI, Escuder MML, Kitoko P, Rea MF, Monteiro CA. Freqüência e determinantes do aleitamento materno em municípios do Estado de São Paulo. Rev Saude Pública. 2002;36(3):313-8. DOI:10.1590/S0034-89102002000300009
-4747. Venancio SI, Monteiro CA. Individual and contextual determinants of exclusive breast-feeding in São Paulo, Brazil: a multilevel analysis. Public Health Nutr. 2006;9(1):40-6. DOI:10.1079/PHN2005760,5151. Vieira GO, Martins CC, Vieira TO, Oliveira NF, Silva LR. Fatores preditivos da interrupção do aleitamento materno exclusivo no primeiro mês de lactação. J Pediatr (Rio J.). 2010;86(5):441-4. DOI:10.1590/S0021-75572010000500015,5252. Vieira TO, Vieira GO, Oliveira NF, Mendes CMC, Giugliani ERJ, Silva LR. Duration of exclusive breastfeeding in a Brazilian population: new determinants in a cohort study. BMC Pregnancy Childbirth. 2014;14(1):175. DOI:10.1186/1471-2393-14-175 (Figure 1), of which seven are cohort studies and 20 are sectional studies. Of these 20, 12 used questionnaires based on the Breastfeeding and Municipalities Project (AMAMUNIC).4848. Venancio SI, Saldiva SR, Mondini L, Levy RB, Escuder MM. Early interruption of exclusive breastfeeding and associated factors, state of São Paulo, Brazil. J Hum Lact. 2008;24(2):168-74. DOI:10.1177/0890334408316073 Considering the classification of the articles selected according to the adapted QATQS scale, of the sectional studies 14 were considered moderate, and six, weak (Table 1). Among the cohort studies, six were considered strong, and only one weak (Table 2).

Figure 1
Descriptive flowchart of steps of systematic review in Medline and LILACS databases.

Table 1
Sectional studies on factors associated with exclusive breastfeeding.
Table 2
Included sectional studies on factors associated with exclusive breastfeeding.

Most of the studies were conducted in towns and covered 77,866 children. Regarding Brazilian regions, 14 studies were carried out in the southeastern, six in the south, five in the Northeast, one in the Midwest, and one in the Northern region. The systematic review included studies conducted between 1998 and 2010 (Tables 1 and 2).

The punctual prevalence of exclusive breastfeeding at six months ranged from 3.9% in Bauru,3030. Parizoto GM, Parada CMGL, Venâncio SI, Carvalhaes MABL. Tendência e determinantes do aleitamento materno exclusivo em crianças menores de 6 meses. J Pediatr (Rio J.). 2009;85(3):201-8. DOI:10.1590/S0021-75572009000300004 SP, Southeastern Brazil, to 8.5% in Pernambuco, Northeastern Brazil, both in 2006.66. Caminha MF, Batista Filho M, Serva VB, Arruda IKG, Figueiroa JN, Lira PIC. Tendências temporais e fatores associados à duração do aleitamento materno em Pernambuco. Rev Saude Publica. 2010;44(2):240-8. DOI:10.1590/S0034-89102010000200003 Regarding the WHO indicator, the prevalence of exclusive breastfeeding in children younger than six months of life, resulting from the survey of this population, ranged from 0% in 10 cities in the state of Sao Paulo, Southeastern Brazil, in 19984646. Venancio SI, Escuder MML, Kitoko P, Rea MF, Monteiro CA. Freqüência e determinantes do aleitamento materno em municípios do Estado de São Paulo. Rev Saude Pública. 2002;36(3):313-8. DOI:10.1590/S0034-89102002000300009 to 58.1% in the city of Rio de Janeiro, Southeastern Brazil, in 20073131. Pereira RSV, Oliveira MIC, Andrade CLT, Brito AS. Fatores associados ao aleitamento materno exclusivo: o papel do cuidado na atenção básica. Cad Saude Publica.2010;26(12):2343-54. DOI:10.1590/S0102-311X2010001200013 (Tables 1 and 2).

Factors associated with exclusive breastfeeding were organized into hierarchical levels (Table 3), being the following the most often exploited (more than a fifth of the 27 studies): place of residence, skin color, maternal age and education, parity, marital status, number of prenatal visits, birth in Baby-Friendly Hospital (BFH), childbirth type, birth weight, sex of the newborn, maternal work, age of the child, financing of the primary health care of the child unit, and the use of a pacifier.

Table 3
Factors investigated regarding the association with exclusive breastfeeding, organized by hierarchical level, frequency of use, and number of times they were associated with exclusive breastfeeding in a statistically significant way.

The factors most frequently associated with exclusive breastfeeding (factors investigated in at least six studies and which have showed association in at least one-third of the studies in which they were investigated) were (according to the category positively associated with the outcome): place of residence (residence in the capital, in the metropolitan area, or in rural areas), intermediate maternal age, maternal education, lack of maternal work, age of the child (descending), the nonuse of a pacifier, and financing of primary health care (private) (Tables 1, 2, and 3).

The studies listed, in total, 36 factors associated with exclusive breastfeeding, 11 classified as distal, four as distal intermediate, nine as proximal intermediate, and 12 as proximal (Table 3).

Of the selected studies, eight used hierarchial theoretical model to identify factors associated with exclusive breastfeeding before starting the statistical modeling, and only one considered contextual variables4747. Venancio SI, Monteiro CA. Individual and contextual determinants of exclusive breast-feeding in São Paulo, Brazil: a multilevel analysis. Public Health Nutr. 2006;9(1):40-6. DOI:10.1079/PHN2005760 (Tables 1 and 2).

Based on the factors listed in the analysis of the 27 selected studies, was created a hierarchial theoretical model of the factors associated with exclusive breastfeeding. Some were constituted of the group of similar factors, such as "difficulties in breastfeeding", which grouped the following variables: nipple fissure, pre-set schedule to breastfeed, and difficulties in latching or positioning. Similarly, were grouped as "emotional indicators" the variables: maternal self-worth and psychological distress (Figure 2).

Figure 2
Hierarchical theoretical model of factors associated with exclusive breastfeeding.

DISCUSSION

A systematic review of Brazilian epidemiologic studies showed a relevant production of studies from the late 1990s having exclusive breastfeeding as outcome, which were conducted mainly in the Southeast region of Brazil. Most of the studies selected for this review showed moderate quality, and only a quarter of the articles had a longitudinal design. Therefore, the evidence of the factors associated with exclusive breastfeeding in children under six months of age in Brazil found in this review can be considered as moderate.

The number of variables listed in epidemiological studies, and used to explain the duration of exclusive breastfeeding, was high, and the discussion of the findings of this systematic review was marked by the organization of the variables in hierarchical levels. Because of the diversity of backgrounds and factors investigated, the use of summary measures of association derived from meta-analysis techniques was considered invalid.

Among distal factors, the place of residence was the contextual variable investigated the most, and the results were discordant, and sometimes the urban environment,2929. Neves ACM, Moura EC, Santos W, Carvalho KMB. Factors associated with exclusive breastfeeding in the Legal Amazon and Northeast regions, Brazil, 2010. Rev Nutr. 2014;27(1):81-95. DOI:10.1590/1415-52732014000100008 sometimes the rural1111. Demétrio F, Pinto EJ, Assis AMO. Fatores associados à interrupção precoce do aleitamento materno: um estudo de coorte de nascimento em dois municípios do Recôncavo da Bahia, Brasil. Cad Saude Publica. 2012;28(4):641-54. DOI:10.1590/S0102-311X2012000400004 were associated with exclusive breastfeeding. Most of distal factors seem to represent maternal socioeconomic factors. Maternal education was the factor most widely investigated, with almost half of the studies having observed an association between maternal education and exclusive breastfeeding, and the findings were unanimous: the low education level was associated with the interruption of exclusive breastfeeding. In epidemiological studies, the socioeconomic gradient is reproduced, in general, in a health gradient.2222. Marmot MG, Kogenivas M, Elston MA. Social/economic status and disease. Ann Rev Public Health. 1987;8(1):111-35. DOI:10.1146/annurev.pu.08.050187.000551 The national research on breastfeeding also report these differences, in which mothers with higher education exclusively breastfeed for more time.d

The variable "skin color or race", in turn, may represent customs, social norms and traditions,2727. Muniz JO. Sobre o uso da variável raça-cor em estudos quantitativos. Rev Sociol Polit. 2010;18(36):277-91. DOI:10.1590/S0104-44782010000200017 besides income88. Cavalieri C, Fernandes R. Diferenciais de salários por gênero e cor: uma comparação entre as regiões metropolitanas brasileiras. Rev Econ Polit. 1998;18(1):158-75. and social relations.e Considering the national surveys, white mothers breastfed exclusively for more time,b b Ministério da Saúde. PNDS 2006: pesquisa nacional de demografia e saúde da criança e da mulher. Brasília (DF): Ministério da Saúde; 2008. but only one study found an association between skin color and higher prevalence of exclusive breastfeeding.3131. Pereira RSV, Oliveira MIC, Andrade CLT, Brito AS. Fatores associados ao aleitamento materno exclusivo: o papel do cuidado na atenção básica. Cad Saude Publica.2010;26(12):2343-54. DOI:10.1590/S0102-311X2010001200013

Maternal age and parity may represent the experience with breastfeeding.3131. Pereira RSV, Oliveira MIC, Andrade CLT, Brito AS. Fatores associados ao aleitamento materno exclusivo: o papel do cuidado na atenção básica. Cad Saude Publica.2010;26(12):2343-54. DOI:10.1590/S0102-311X2010001200013,5151. Vieira GO, Martins CC, Vieira TO, Oliveira NF, Silva LR. Fatores preditivos da interrupção do aleitamento materno exclusivo no primeiro mês de lactação. J Pediatr (Rio J.). 2010;86(5):441-4. DOI:10.1590/S0021-75572010000500015 All studies that investigated them observed an association between greater parity and exclusive breastfeeding.1616. França GVA, Brunken GS, Silva SM, Escuder MM, Venancio SI. Determinantes da amamentação no primeiro ano de vida em Cuiabá, Mato Grosso. Rev Saude Publica. 2007;41(5):711-8. DOI:10.1590/S0034-89102007000500004,1818. Gusmão AM, Béria JU, Gigante LP, Leal AF, Schermann LB. Prevalência de aleitamento materno exclusivo e fatores associados: estudo transversal com mães adolescentes de 14 a 16 anos em Porto Alegre, RS, Brasil. Cien Saude Colet. 2013;18(11):3357-68. DOI:10.1590/S1413-81232013001100025,2323. Martins CC, Vieira GO, Vieira TO, Mendes CM. Fatores de riscos maternos e de assistência ao parto para interrupção precoce do aleitamento materno exclusivo: estudo de coorte. Rev Baiana Saude Publica. 2011;35(Supl 1):167-8.,4444. Vannuchi MTO, Thomson Z, Escuder MML, Tacia MTGM, Venozzo KMK, Castro LMCP, Oliveira MBM, Venancio SI. Perfil do aleitamento materno em menores de um ano no Município de Londrina, Paraná. Rev Bras Saude Mater Infant. 2005;5(2):155-62. DOI:10.1590/S1519-38292005000200003,4646. Venancio SI, Escuder MML, Kitoko P, Rea MF, Monteiro CA. Freqüência e determinantes do aleitamento materno em municípios do Estado de São Paulo. Rev Saude Pública. 2002;36(3):313-8. DOI:10.1590/S0034-89102002000300009,4747. Venancio SI, Monteiro CA. Individual and contextual determinants of exclusive breast-feeding in São Paulo, Brazil: a multilevel analysis. Public Health Nutr. 2006;9(1):40-6. DOI:10.1079/PHN2005760 Regarding maternal age, the intermediate ages seem to be protective for exclusive breastfeeding, because both teenage mothers55. Bueno MB, Souza JM, Souza SB, Paz SM, Gimeno SG, Siqueira AA. Riscos associados ao processo de desmame entre crianças nascidas em hospital universitário de São Paulo, entre 1998 e 1999: estudo de coorte prospectivo do primeiro ano de vida. Cad Saude Publica. 2003;19(5):1453-60. DOI:10.1590/S0102-311X2003000500024,2929. Neves ACM, Moura EC, Santos W, Carvalho KMB. Factors associated with exclusive breastfeeding in the Legal Amazon and Northeast regions, Brazil, 2010. Rev Nutr. 2014;27(1):81-95. DOI:10.1590/1415-52732014000100008,4040. Santo LC, Oliveira LD, Giugliani ER. Factors associated with low incidence of exclusive breastfeeding for the first 6 months. Birth. 2007;34(3):212-9. DOI:10.1111/j.1523-536X.2007.00173.x,4646. Venancio SI, Escuder MML, Kitoko P, Rea MF, Monteiro CA. Freqüência e determinantes do aleitamento materno em municípios do Estado de São Paulo. Rev Saude Pública. 2002;36(3):313-8. DOI:10.1590/S0034-89102002000300009,4747. Venancio SI, Monteiro CA. Individual and contextual determinants of exclusive breast-feeding in São Paulo, Brazil: a multilevel analysis. Public Health Nutr. 2006;9(1):40-6. DOI:10.1079/PHN2005760 and those with 35 years of age or more66. Caminha MF, Batista Filho M, Serva VB, Arruda IKG, Figueiroa JN, Lira PIC. Tendências temporais e fatores associados à duração do aleitamento materno em Pernambuco. Rev Saude Publica. 2010;44(2):240-8. DOI:10.1590/S0034-89102010000200003,1010. Damião JJ. Influência da escolaridade e do trabalho maternos no aleitamento materno exclusivo. Rev Bras Epidemiol. 2008;11(3):442-52. DOI:10.1590/S1415-790X200800030001,1616. França GVA, Brunken GS, Silva SM, Escuder MM, Venancio SI. Determinantes da amamentação no primeiro ano de vida em Cuiabá, Mato Grosso. Rev Saude Publica. 2007;41(5):711-8. DOI:10.1590/S0034-89102007000500004 interrupt it prematurely.

Considering the distal intermediate factors concerning pregnancy, the number of prenatal visits was the variable most frequently investigated. The three studies that found an association between this variable and the outcome indicated the low number of prenatal visits as a risk factor for exclusive breastfeeding. Santo et al4040. Santo LC, Oliveira LD, Giugliani ER. Factors associated with low incidence of exclusive breastfeeding for the first 6 months. Birth. 2007;34(3):212-9. DOI:10.1111/j.1523-536X.2007.00173.x and Vieira et al5252. Vieira TO, Vieira GO, Oliveira NF, Mendes CMC, Giugliani ERJ, Silva LR. Duration of exclusive breastfeeding in a Brazilian population: new determinants in a cohort study. BMC Pregnancy Childbirth. 2014;14(1):175. DOI:10.1186/1471-2393-14-175 consider that low compliance to prenatal care may represent women who are less careful with their health; on the other hand, Demétrio et al1111. Demétrio F, Pinto EJ, Assis AMO. Fatores associados à interrupção precoce do aleitamento materno: um estudo de coorte de nascimento em dois municípios do Recôncavo da Bahia, Brasil. Cad Saude Publica. 2012;28(4):641-54. DOI:10.1590/S0102-311X2012000400004 consider that this low compliance may reflect low access to sources of information on breastfeeding.

The public or private service pervades all hierarchical levels evaluated: prenatal care (distal intermediate level), childbirth (proximal intermediate), and childcare (proximal). The private primary care was associated with the outcome in three of 10 studies.4444. Vannuchi MTO, Thomson Z, Escuder MML, Tacia MTGM, Venozzo KMK, Castro LMCP, Oliveira MBM, Venancio SI. Perfil do aleitamento materno em menores de um ano no Município de Londrina, Paraná. Rev Bras Saude Mater Infant. 2005;5(2):155-62. DOI:10.1590/S1519-38292005000200003,4747. Venancio SI, Monteiro CA. Individual and contextual determinants of exclusive breast-feeding in São Paulo, Brazil: a multilevel analysis. Public Health Nutr. 2006;9(1):40-6. DOI:10.1079/PHN2005760,5252. Vieira TO, Vieira GO, Oliveira NF, Mendes CMC, Giugliani ERJ, Silva LR. Duration of exclusive breastfeeding in a Brazilian population: new determinants in a cohort study. BMC Pregnancy Childbirth. 2014;14(1):175. DOI:10.1186/1471-2393-14-175 This variable may represent both the access to health services and the maternal socioeconomic status, for the access to health services may be determined by more distal variables such as skin color, sex, education, and income.3636. Ribeiro MCSA, Barata RB, Almeida MF, Silva ZP. Perfil sociodemográfico e padrão de utilização de serviços de saúde para usuários e não-usuários do SUS - PNAD 2003. Cien Saude Colet. 2006;11(4):1011-22. DOI:10.1590/S1413-81232006000400022

Among the proximal intermediate factors, the birth weight was the one most widely used, finding a positive association between children with adequate birth weight and exclusive breastfeeding in three of the 21 studies that investigated it.99. Chaves RG, Lamounier JA, César CC. Fatores associados com a duração do aleitamento materno. J Pediatr (Rio J.). 2007;83(3):241-6. DOI:10.1590/S0021-75572007000400009,4444. Vannuchi MTO, Thomson Z, Escuder MML, Tacia MTGM, Venozzo KMK, Castro LMCP, Oliveira MBM, Venancio SI. Perfil do aleitamento materno em menores de um ano no Município de Londrina, Paraná. Rev Bras Saude Mater Infant. 2005;5(2):155-62. DOI:10.1590/S1519-38292005000200003,4747. Venancio SI, Monteiro CA. Individual and contextual determinants of exclusive breast-feeding in São Paulo, Brazil: a multilevel analysis. Public Health Nutr. 2006;9(1):40-6. DOI:10.1079/PHN2005760 This may be explained because children with low birth weight are more likely to spend more time hospitalized in neonatal unit, thus spending more time separated from their mothers.4141. Serra SO, Scochi CG. Dificuldades maternas no processo de aleitamento materno de prematuros em uma UTI neonatal. Rev Lat Am Enfermagem. 2004;12(4):597-605. DOI:10.1590/S0104-11692004000400004 In addition, these children may have more difficulties in initiating or maintaining breastfeeding, since both the frequency and the pressure of the suction increase as the gestational age and weight of newborn increase.2525. Medoff-Cooper B, Verklan T, Carlson S. The development of sucking patterns and physiologic correlates in very-low-birth-weight infants. Nurs Res 1993;42(2):100-5. DOI:10.1097/00006199-199303000-00007

Gestational age, in turn, was an indicator hardly used in the studies, for differences or biases in the rankings of this variable that may occur.4242. Silva AAM, Ribeiro VS, Borba Júnior AF, Coimbra LC, Silva RA. Avaliação da qualidade dos dados do Sistema de Informações sobre Nascidos Vivos em 1997-1998. Rev Saude Publica. 2001;35(6):508-14. DOI:10.1590/S0034-89102001000600003 Although no studies have found an association between this variable and the outcome, it is suggested to maintain it in the studies.

Another factor widely used in the studies was the childbirth type, however, only two studies have found an association between the vaginal childbirth and higher prevalence of exclusive breastfeeding.11. Alves ALN, Oliveira MIC, Moraes JR. Iniciativa Unidade Básica Amiga da Amamentação e sua relação com o aleitamento materno exclusivo. Rev Saude Publica. 2013;47(6):1130-40. DOI:10.1590/S0034-89102013000901130,22. Audi CAF, Corrêa AMS, Latorre MRDO. Alimentos complementares e fatores associados ao aleitamento materno e ao aleitamento materno exclusivo em lactentes até 12 m de vida em Itapira, SP, 1999. Rev Bras Saude Mater Infant. 2003;3(1):85-93. DOI:10.1590/S1519-38292003000100011 The vaginal childbirth contributes to the timely initiation of breastfeeding,33. Boccolini CS, Carvalho ML, Oliveira MIC, Leal MC, Carvalho MS. Fatores que interferem no tempo entre o nascimento e a primeira mamada. Cad Saude Publica. 2008;24(11):2681-94. DOI:10.1590/S0102-311X2008001100023 being possible to assume that it can also provide its maintenance in exclusive mode. Another hypothesis would be the possible relationship between socioeconomic characteristics and access to public health services,1717. Freitas PF, Drachler ML, Leite JC, Grassi PR. Desigualdade social nas taxas de cesariana em primíparas no Rio Grande do Sul. Rev Saude Publica. 2005;39(5):761-7. DOI:10.1590/S0034-89102005000500010 since both the vaginal childbirth1313. Domingues RM, Dias MA, Nakamura-Pereira M, Torres JA, d'Orsi E, Pereira AP et al. rocesso de decisão pelo tipo de parto no Brasil: da preferência inicial das mulheres à via de parto final. Cad Saude Publica. 2014;30(Supl 1):S101-16. DOI:10.1590/0102-311X00105113 and timely initiation of breastfeeding are more practiced at these services.33. Boccolini CS, Carvalho ML, Oliveira MIC, Leal MC, Carvalho MS. Fatores que interferem no tempo entre o nascimento e a primeira mamada. Cad Saude Publica. 2008;24(11):2681-94. DOI:10.1590/S0102-311X2008001100023

Among the proximal intermediate factors studied, those that assess the guidelines received in hospital2323. Martins CC, Vieira GO, Vieira TO, Mendes CM. Fatores de riscos maternos e de assistência ao parto para interrupção precoce do aleitamento materno exclusivo: estudo de coorte. Rev Baiana Saude Publica. 2011;35(Supl 1):167-8.,5252. Vieira TO, Vieira GO, Oliveira NF, Mendes CMC, Giugliani ERJ, Silva LR. Duration of exclusive breastfeeding in a Brazilian population: new determinants in a cohort study. BMC Pregnancy Childbirth. 2014;14(1):175. DOI:10.1186/1471-2393-14-175 (positive association with the outcome), the difficulties to breastfeed during hospitalization77. Carvalhaes MABL, Parada CMGL, Costa MP. Fatores associados à situação do aleitamento materno exclusivo em crianças menores de 4 meses, em Botucatu - SP. Rev Lat Am Enfermagem. 2007;15(1):62-9. DOI:10.1590/S0104-11692007000100010 (negative association), and exclusive breastfeeding on discharge3131. Pereira RSV, Oliveira MIC, Andrade CLT, Brito AS. Fatores associados ao aleitamento materno exclusivo: o papel do cuidado na atenção básica. Cad Saude Publica.2010;26(12):2343-54. DOI:10.1590/S0102-311X2010001200013 (positive association) may be the most adequate to evaluate peri-partum related aspects which may determine the duration of exclusive breastfeeding.

The variable "sex of the baby" was used in 14 studies, considering that two66. Caminha MF, Batista Filho M, Serva VB, Arruda IKG, Figueiroa JN, Lira PIC. Tendências temporais e fatores associados à duração do aleitamento materno em Pernambuco. Rev Saude Publica. 2010;44(2):240-8. DOI:10.1590/S0034-89102010000200003,4747. Venancio SI, Monteiro CA. Individual and contextual determinants of exclusive breast-feeding in São Paulo, Brazil: a multilevel analysis. Public Health Nutr. 2006;9(1):40-6. DOI:10.1079/PHN2005760 found a positive association between female and one between male55. Bueno MB, Souza JM, Souza SB, Paz SM, Gimeno SG, Siqueira AA. Riscos associados ao processo de desmame entre crianças nascidas em hospital universitário de São Paulo, entre 1998 e 1999: estudo de coorte prospectivo do primeiro ano de vida. Cad Saude Publica. 2003;19(5):1453-60. DOI:10.1590/S0102-311X2003000500024 and exclusive breastfeeding. The prevalence of breastfeeding among girls was higher in the capitals of the entire Brazil;b b Ministério da Saúde. PNDS 2006: pesquisa nacional de demografia e saúde da criança e da mulher. Brasília (DF): Ministério da Saúde; 2008. however, it is unclear whether this increased prevalence is due to some cultural aspect such as the belief that boys need greater nutritional intake by other foods in addition to breast milk.3232. Pérez-Escamilla R, Lutter C, Segall AM, Rivera A, Treviño-Siller S, Sanghvi T. Exclusive breast-feeding duration is associated with attitudinal, socioeconomic and biocultural determinants in three Latin American countries. J Nutr. 1995;125(12):2972-84.,4747. Venancio SI, Monteiro CA. Individual and contextual determinants of exclusive breast-feeding in São Paulo, Brazil: a multilevel analysis. Public Health Nutr. 2006;9(1):40-6. DOI:10.1079/PHN2005760

Regarding the proximal factors considered, the use of a pacifier was the factor most strongly associated with the interruption of exclusive breastfeeding.22. Audi CAF, Corrêa AMS, Latorre MRDO. Alimentos complementares e fatores associados ao aleitamento materno e ao aleitamento materno exclusivo em lactentes até 12 m de vida em Itapira, SP, 1999. Rev Bras Saude Mater Infant. 2003;3(1):85-93. DOI:10.1590/S1519-38292003000100011,77. Carvalhaes MABL, Parada CMGL, Costa MP. Fatores associados à situação do aleitamento materno exclusivo em crianças menores de 4 meses, em Botucatu - SP. Rev Lat Am Enfermagem. 2007;15(1):62-9. DOI:10.1590/S0104-11692007000100010,99. Chaves RG, Lamounier JA, César CC. Fatores associados com a duração do aleitamento materno. J Pediatr (Rio J.). 2007;83(3):241-6. DOI:10.1590/S0021-75572007000400009,1616. França GVA, Brunken GS, Silva SM, Escuder MM, Venancio SI. Determinantes da amamentação no primeiro ano de vida em Cuiabá, Mato Grosso. Rev Saude Publica. 2007;41(5):711-8. DOI:10.1590/S0034-89102007000500004,2121. Leone CR, Sadeck LSR. Fatores de risco associados ao desmame em crianças até seis meses de idade no município de São Paulo. Rev Paul Pediatr. 2012;30(1):21-6. DOI:10.1590/S0103-05822012000100004,2424. Mascarenhas MLW, Albernaz EP, Silva MB, Silveira RB. Prevalência de aleitamento materno exclusivo nos 3 primeiros meses de vida e seus determinantes no Sul do Brasil. J Pediatr (Rio J.). 2006;82(4):289-94. DOI:10.1590/S0021-75572006000500011,2828. Nascimento MBR, Reis MAM, Franco SC, Issler H, Ferraro AA, Grisi SJFE. Exclusive breastfeeding in southern Brazil: prevalence and associated factors. Breastfeed Med. 2010;5(2):79-85. DOI:10.1089/bfm.2009.0008,3030. Parizoto GM, Parada CMGL, Venâncio SI, Carvalhaes MABL. Tendência e determinantes do aleitamento materno exclusivo em crianças menores de 6 meses. J Pediatr (Rio J.). 2009;85(3):201-8. DOI:10.1590/S0021-75572009000300004,4343. Silva MB, Albernaz EP, Mascarenhas MLW, Silveira RB. Influência do apoio à amamentação sobre o aleitamento materno exclusivo dos bebês no primeiro mês de vida e nascidos na cidade de Pelotas, Rio Grande do Sul, Brasil. Rev Bras Saude Mater Infant. 2008;8(3):275-84. DOI:10.1590/S1519-38292008000300006,4444. Vannuchi MTO, Thomson Z, Escuder MML, Tacia MTGM, Venozzo KMK, Castro LMCP, Oliveira MBM, Venancio SI. Perfil do aleitamento materno em menores de um ano no Município de Londrina, Paraná. Rev Bras Saude Mater Infant. 2005;5(2):155-62. DOI:10.1590/S1519-38292005000200003,5151. Vieira GO, Martins CC, Vieira TO, Oliveira NF, Silva LR. Fatores preditivos da interrupção do aleitamento materno exclusivo no primeiro mês de lactação. J Pediatr (Rio J.). 2010;86(5):441-4. DOI:10.1590/S0021-75572010000500015,5252. Vieira TO, Vieira GO, Oliveira NF, Mendes CMC, Giugliani ERJ, Silva LR. Duration of exclusive breastfeeding in a Brazilian population: new determinants in a cohort study. BMC Pregnancy Childbirth. 2014;14(1):175. DOI:10.1186/1471-2393-14-175 The use of a pacifier may lead to the reduction in breastfeeding frequency, interfering in breast demand, and possibly changing the baby's oral dynamics.5050. Victora CG, Behague DP, Barros FC, Olinto MT, Weiderpass E. Pacifier use and short breastfeeding duration: cause, consequence, or coincidence? Pediatrics. 1997;99(3):445-53. DOI:10.1542/peds.99.3.445 A Brazilian study concluded that, in addition to the causal relationship between the use of a pacifier and breastfeeding interruption be unclear (it is unknown whether the use of a pacifier is a marker of the interruption of breastfeeding, or if it is a cause of the same), the process of using pacifiers is dynamic, with children starting or stopping the use of a pacifier throughout the period.5050. Victora CG, Behague DP, Barros FC, Olinto MT, Weiderpass E. Pacifier use and short breastfeeding duration: cause, consequence, or coincidence? Pediatrics. 1997;99(3):445-53. DOI:10.1542/peds.99.3.445 In a randomized study conducted in Canada,1919. Kramer MS, Barr RG, Dagenais S, Yang H, Jones P, Ciofani L et al. Pacifier use, early weaning, and cry/fuss behavior: a randomized controlled trial. JAMA. 2001;286(3):322-6. DOI:10.1001/jama.286.3.322 the authors observed that the use of a pacifier can be a marker of the interruption of breastfeeding or of low motivation to breastfeed rather than be the cause of the interruption of breastfeeding.

Maternal work was a variable widely used in studies,11. Alves ALN, Oliveira MIC, Moraes JR. Iniciativa Unidade Básica Amiga da Amamentação e sua relação com o aleitamento materno exclusivo. Rev Saude Publica. 2013;47(6):1130-40. DOI:10.1590/S0034-89102013000901130,22. Audi CAF, Corrêa AMS, Latorre MRDO. Alimentos complementares e fatores associados ao aleitamento materno e ao aleitamento materno exclusivo em lactentes até 12 m de vida em Itapira, SP, 1999. Rev Bras Saude Mater Infant. 2003;3(1):85-93. DOI:10.1590/S1519-38292003000100011,66. Caminha MF, Batista Filho M, Serva VB, Arruda IKG, Figueiroa JN, Lira PIC. Tendências temporais e fatores associados à duração do aleitamento materno em Pernambuco. Rev Saude Publica. 2010;44(2):240-8. DOI:10.1590/S0034-89102010000200003,77. Carvalhaes MABL, Parada CMGL, Costa MP. Fatores associados à situação do aleitamento materno exclusivo em crianças menores de 4 meses, em Botucatu - SP. Rev Lat Am Enfermagem. 2007;15(1):62-9. DOI:10.1590/S0104-11692007000100010,99. Chaves RG, Lamounier JA, César CC. Fatores associados com a duração do aleitamento materno. J Pediatr (Rio J.). 2007;83(3):241-6. DOI:10.1590/S0021-75572007000400009

10. Damião JJ. Influência da escolaridade e do trabalho maternos no aleitamento materno exclusivo. Rev Bras Epidemiol. 2008;11(3):442-52. DOI:10.1590/S1415-790X200800030001
-1111. Demétrio F, Pinto EJ, Assis AMO. Fatores associados à interrupção precoce do aleitamento materno: um estudo de coorte de nascimento em dois municípios do Recôncavo da Bahia, Brasil. Cad Saude Publica. 2012;28(4):641-54. DOI:10.1590/S0102-311X2012000400004,1616. França GVA, Brunken GS, Silva SM, Escuder MM, Venancio SI. Determinantes da amamentação no primeiro ano de vida em Cuiabá, Mato Grosso. Rev Saude Publica. 2007;41(5):711-8. DOI:10.1590/S0034-89102007000500004,2121. Leone CR, Sadeck LSR. Fatores de risco associados ao desmame em crianças até seis meses de idade no município de São Paulo. Rev Paul Pediatr. 2012;30(1):21-6. DOI:10.1590/S0103-05822012000100004,2424. Mascarenhas MLW, Albernaz EP, Silva MB, Silveira RB. Prevalência de aleitamento materno exclusivo nos 3 primeiros meses de vida e seus determinantes no Sul do Brasil. J Pediatr (Rio J.). 2006;82(4):289-94. DOI:10.1590/S0021-75572006000500011,2828. Nascimento MBR, Reis MAM, Franco SC, Issler H, Ferraro AA, Grisi SJFE. Exclusive breastfeeding in southern Brazil: prevalence and associated factors. Breastfeed Med. 2010;5(2):79-85. DOI:10.1089/bfm.2009.0008,3030. Parizoto GM, Parada CMGL, Venâncio SI, Carvalhaes MABL. Tendência e determinantes do aleitamento materno exclusivo em crianças menores de 6 meses. J Pediatr (Rio J.). 2009;85(3):201-8. DOI:10.1590/S0021-75572009000300004,3131. Pereira RSV, Oliveira MIC, Andrade CLT, Brito AS. Fatores associados ao aleitamento materno exclusivo: o papel do cuidado na atenção básica. Cad Saude Publica.2010;26(12):2343-54. DOI:10.1590/S0102-311X2010001200013,3434. Queluz MC, Pereira MJB, Santos CB, Leite AM, Ricco RG. Prevalência e determinantes do aleitamento materno exclusivo no município de Serrana, São Paulo, Brasil. Rev Esc Enferm USP. 2012;46(3):537-43. DOI:10.1590/S0080-62342012000300002,3838. Rito RVVF, Oliveira MIC, Brito AS. Grau de cumprimento dos Dez Passos da Iniciativa Unidade Básica Amiga da Amamentação e sua associação com a prevalência de aleitamento materno exclusivo. J Pediatr (Rio J). 2013;89(5):477-84. DOI:10.1016/j.jped.2013.02.018,4343. Silva MB, Albernaz EP, Mascarenhas MLW, Silveira RB. Influência do apoio à amamentação sobre o aleitamento materno exclusivo dos bebês no primeiro mês de vida e nascidos na cidade de Pelotas, Rio Grande do Sul, Brasil. Rev Bras Saude Mater Infant. 2008;8(3):275-84. DOI:10.1590/S1519-38292008000300006

44. Vannuchi MTO, Thomson Z, Escuder MML, Tacia MTGM, Venozzo KMK, Castro LMCP, Oliveira MBM, Venancio SI. Perfil do aleitamento materno em menores de um ano no Município de Londrina, Paraná. Rev Bras Saude Mater Infant. 2005;5(2):155-62. DOI:10.1590/S1519-38292005000200003

45. Venancio SI, Monteiro CA. A tendência da prática da amamentação no Brasil nas décadas de 70 e 80. Rev Bras Epidemiol. 1998;1(1):40-9. DOI:10.1590/S1415-790X1998000100005

46. Venancio SI, Escuder MML, Kitoko P, Rea MF, Monteiro CA. Freqüência e determinantes do aleitamento materno em municípios do Estado de São Paulo. Rev Saude Pública. 2002;36(3):313-8. DOI:10.1590/S0034-89102002000300009
-4747. Venancio SI, Monteiro CA. Individual and contextual determinants of exclusive breast-feeding in São Paulo, Brazil: a multilevel analysis. Public Health Nutr. 2006;9(1):40-6. DOI:10.1079/PHN2005760,5252. Vieira TO, Vieira GO, Oliveira NF, Mendes CMC, Giugliani ERJ, Silva LR. Duration of exclusive breastfeeding in a Brazilian population: new determinants in a cohort study. BMC Pregnancy Childbirth. 2014;14(1):175. DOI:10.1186/1471-2393-14-175 and in the six studies that found statistically significant association, it showed a negative association with the outcome. However, this variable must be investigated considering if the mother is or is not on maternity leave.5151. Vieira GO, Martins CC, Vieira TO, Oliveira NF, Silva LR. Fatores preditivos da interrupção do aleitamento materno exclusivo no primeiro mês de lactação. J Pediatr (Rio J.). 2010;86(5):441-4. DOI:10.1590/S0021-75572010000500015 Mothers that work outside the home with maternity leave would have better conditions to maintain exclusive breastfeeding during the maternity leave period.

Most of the studies based on surveys did not consider the child's age, but the probability to be exclusively breastfed decreases as the age of the child increases. All the studies that used this variable found an association between the descending age (or early age) of the child and exclusive breastfeeding.11. Alves ALN, Oliveira MIC, Moraes JR. Iniciativa Unidade Básica Amiga da Amamentação e sua relação com o aleitamento materno exclusivo. Rev Saude Publica. 2013;47(6):1130-40. DOI:10.1590/S0034-89102013000901130,1010. Damião JJ. Influência da escolaridade e do trabalho maternos no aleitamento materno exclusivo. Rev Bras Epidemiol. 2008;11(3):442-52. DOI:10.1590/S1415-790X200800030001,1818. Gusmão AM, Béria JU, Gigante LP, Leal AF, Schermann LB. Prevalência de aleitamento materno exclusivo e fatores associados: estudo transversal com mães adolescentes de 14 a 16 anos em Porto Alegre, RS, Brasil. Cien Saude Colet. 2013;18(11):3357-68. DOI:10.1590/S1413-81232013001100025,2121. Leone CR, Sadeck LSR. Fatores de risco associados ao desmame em crianças até seis meses de idade no município de São Paulo. Rev Paul Pediatr. 2012;30(1):21-6. DOI:10.1590/S0103-05822012000100004,2828. Nascimento MBR, Reis MAM, Franco SC, Issler H, Ferraro AA, Grisi SJFE. Exclusive breastfeeding in southern Brazil: prevalence and associated factors. Breastfeed Med. 2010;5(2):79-85. DOI:10.1089/bfm.2009.0008,2929. Neves ACM, Moura EC, Santos W, Carvalho KMB. Factors associated with exclusive breastfeeding in the Legal Amazon and Northeast regions, Brazil, 2010. Rev Nutr. 2014;27(1):81-95. DOI:10.1590/1415-52732014000100008,3131. Pereira RSV, Oliveira MIC, Andrade CLT, Brito AS. Fatores associados ao aleitamento materno exclusivo: o papel do cuidado na atenção básica. Cad Saude Publica.2010;26(12):2343-54. DOI:10.1590/S0102-311X2010001200013,4444. Vannuchi MTO, Thomson Z, Escuder MML, Tacia MTGM, Venozzo KMK, Castro LMCP, Oliveira MBM, Venancio SI. Perfil do aleitamento materno em menores de um ano no Município de Londrina, Paraná. Rev Bras Saude Mater Infant. 2005;5(2):155-62. DOI:10.1590/S1519-38292005000200003

Among all the variables considered proximal, those that evaluate the access to information or guidance on breastfeeding that women receive in primary health care services could be those more directly associated with exclusive breastfeeding. However, only Pereira et al3131. Pereira RSV, Oliveira MIC, Andrade CLT, Brito AS. Fatores associados ao aleitamento materno exclusivo: o papel do cuidado na atenção básica. Cad Saude Publica.2010;26(12):2343-54. DOI:10.1590/S0102-311X2010001200013 used this variable, noting that guidelines in group and on positioning and latching of the baby were associated with a higher prevalence of exclusive breastfeeding.

Evaluating statistical modeling strategies, less than a quarter of the studies included in this review adopted a theoretical model prior to analysis, organizing the variables in hierarchical levels.66. Caminha MF, Batista Filho M, Serva VB, Arruda IKG, Figueiroa JN, Lira PIC. Tendências temporais e fatores associados à duração do aleitamento materno em Pernambuco. Rev Saude Publica. 2010;44(2):240-8. DOI:10.1590/S0034-89102010000200003,77. Carvalhaes MABL, Parada CMGL, Costa MP. Fatores associados à situação do aleitamento materno exclusivo em crianças menores de 4 meses, em Botucatu - SP. Rev Lat Am Enfermagem. 2007;15(1):62-9. DOI:10.1590/S0104-11692007000100010,1818. Gusmão AM, Béria JU, Gigante LP, Leal AF, Schermann LB. Prevalência de aleitamento materno exclusivo e fatores associados: estudo transversal com mães adolescentes de 14 a 16 anos em Porto Alegre, RS, Brasil. Cien Saude Colet. 2013;18(11):3357-68. DOI:10.1590/S1413-81232013001100025,2424. Mascarenhas MLW, Albernaz EP, Silva MB, Silveira RB. Prevalência de aleitamento materno exclusivo nos 3 primeiros meses de vida e seus determinantes no Sul do Brasil. J Pediatr (Rio J.). 2006;82(4):289-94. DOI:10.1590/S0021-75572006000500011,3131. Pereira RSV, Oliveira MIC, Andrade CLT, Brito AS. Fatores associados ao aleitamento materno exclusivo: o papel do cuidado na atenção básica. Cad Saude Publica.2010;26(12):2343-54. DOI:10.1590/S0102-311X2010001200013,4343. Silva MB, Albernaz EP, Mascarenhas MLW, Silveira RB. Influência do apoio à amamentação sobre o aleitamento materno exclusivo dos bebês no primeiro mês de vida e nascidos na cidade de Pelotas, Rio Grande do Sul, Brasil. Rev Bras Saude Mater Infant. 2008;8(3):275-84. DOI:10.1590/S1519-38292008000300006,5252. Vieira TO, Vieira GO, Oliveira NF, Mendes CMC, Giugliani ERJ, Silva LR. Duration of exclusive breastfeeding in a Brazilian population: new determinants in a cohort study. BMC Pregnancy Childbirth. 2014;14(1):175. DOI:10.1186/1471-2393-14-175 Although expendable, to create this conceptual model is important because it requires prior knowledge about the social and biological factors associated with outcome, assisting to establish an order of logic input variables in the model based on hierarchy of factors and not considering only purely statistical criteria.4949. Victora CG, Huttly SR, Fuchs SC, Olinto MTA. The role of conceptual frameworks in epidemiological analysis: a hierarchical approach. Int J Epidemiol. 1997;26(1):224-7. DOI:10.1093/ije/26.1.224 Thus, a hierarchical theoretical model was proposed, including factors identified in the studies of this systematic review, which can assist in planning data collection and statistical modeling strategy of epidemiological studies related to exclusive breastfeeding.

Public policies to promote, protect, and support breastfeeding adopted in Brazil since the 1980s have contributed to the increase in the median duration of breastfeeding and its exclusive mode across the Country.3535. Rea MF. Reflexões sobre a amamentação no Brasil: de como passamos a 10 meses de duração. Cad Saude Publica. 2003;19(Supl 1):S37-45. DOI:10.1590/S0102-311X2003000700005 These policies, however, cannot be considered as an individual attribute: having a childbirth in Baby-Friendly Hospital or maternity with Human Milk Bank may depend on the context in which the woman lives as well as her access to these services.

In addition, the local contexts within each city (districts, neighborhoods, surroundings) may vary: in the city of Rio de Janeiro, e.g., a great variation in the adoption of the 10 steps to successful breastfeeding (recommended by the Breastfeeding-Friendly Primary Care Unit Initiative) are found between the units of primary health network.3737. Rito RVVF, Castro IRR, Trajano AJB, Gomes MASM, Bernal RTI. Breastfeeding-Friendly Primary Care Initiative: degree of implementation in a Brazilian metropolis. Rev Nutr. 2013;26(4):385-95. DOI:10.1590/S1415-52732013000400001 In addition, disparities between public and private health units must be considered, such as those observed in the adoption of breastfeeding in the first hour of life in hospitals (recommended by the Baby-Friendly Hospital Initiative).33. Boccolini CS, Carvalho ML, Oliveira MIC, Leal MC, Carvalho MS. Fatores que interferem no tempo entre o nascimento e a primeira mamada. Cad Saude Publica. 2008;24(11):2681-94. DOI:10.1590/S0102-311X2008001100023

Considering this possible context effect, it is plausible that nursing mothers who are residing in the same regions or municipalities (including districts, neighborhoods, or census units) share social and economic factors (contextual factors) that influence the duration of exclusive breastfeeding, e.g., standards and attitudes toward breastfeeding; the organization and access to primary health services in their neighborhood; and the level of action and policies for promoting, protecting, and supporting breastfeeding. In fact, variables such as socioeconomic indexes and the number of pro-breastfeeding actions existent in certain regions have already been used for the evaluation of factors associated with exclusive breastfeeding.4747. Venancio SI, Monteiro CA. Individual and contextual determinants of exclusive breast-feeding in São Paulo, Brazil: a multilevel analysis. Public Health Nutr. 2006;9(1):40-6. DOI:10.1079/PHN2005760

Many factors used in analytical epidemiological studies and its directionality in association with exclusive breastfeeding were identified and described, noting the frequency with which they are used and the heterogeneity of categories and cutoff points. Instead of defining the effect of each of the factors identified in the systematic review by meta-analysis, we decided to discuss them according to a hierarchical theoretical model.

Some recommendations concerning the findings of this study include the completion of further studies in the North and Midwest of the Country, as well as the encouragement to academic work on little explored factors in association with exclusive breastfeeding.

The use of a conceptual theoretical model prior to statistical analysis, preferring the hierarchical organization of variables in relation to the proximity to the outcome, may help the choice of variables to be included in the studies and to evaluate the intermediation of more proximal variable blocks in relation to the more distal ones.

It is suggested that future studies consider context variables to investigate the association with exclusive breastfeeding, since inclusion of contextual variables with concomitant multilevel models is a useful strategy for the adequacy of these models.1212. Diez-Roux AV. Multilevel analysis in public health research. Annu Rev Public Health. 2000;21(1):171-92. DOI:10.1146/annurev.publhealth.21.1.171 Studies covering the triangulation of qualitative and quantitative methods2626. Minayo MC, Assis SGD, Souza ERD, organizadores. Avaliação por triangulação de métodos: abordagem de programas sociais. Rio de Janeiro: Fiocruz; 2005. to the understanding of the relation of some factors with exclusive breastfeeding could also contribute to a better understanding of the subject.

The main limitation of this systematic review was the selection bias, since abstracts published in conference proceedings were not included, which is called the "grey literature".3333. Población DA, Noronha DP. Produção das literaturas "branca" e "cinzenta" pelos docentes/doutores dos programas de pós-graduação em ciência da informação no Brasil. Cienc Inform. 2002;31(2):98-106. DOI:10.1590/S0100-19652002000200011 Another limitation is the possibility that relevant studies have not been found by the search strategy used. The possible subjectivity of the authors in the evaluation and selection of articles was minimized by the independent search of the literature, by the standardized form-filling, and by assessing the quality of the articles selected for the review.

In conclusion, the study of determinants of exclusive breastfeeding is of vital importance for public health, and epidemiological studies have an important role for the understanding of this theme in Brazil. However, the emergence of new and more sophisticated statistical tools, as well as the growing complexity of explanatory models and the context effects of the factors associated with exclusive breastfeeding, brings a new challenge to scholars of the topic: the careful use of these resources and the dissemination of the results in a clear and purposeful way, directed to the development and improvement of public policies for promoting, protecting, and supporting breastfeeding which are reflected in the health and well-being of the population.

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    World Health Organization. Indicators for assessing infant and young child feeding practices. Part 1: definitions. Conclusions of a consensus meeting held 6-8 November 2007 in Washington, DC, USA. Geneva: World Health Organization; 2007.

Publication Dates

  • Publication in this collection
    2015

History

  • Received
    11 June 2015
  • Accepted
    4 Dec 2015
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