Introduction

Exclusive breastfeeding (EBF) in the first 6 months of life is considered the most complete diet for newborns, as it provides all the energy, vitamins, and minerals that infants need. After this period, breastfeeding must continue until at least 2 years of age, even after the introduction of solid foods.¹ This is because it is the most economical and effective form of protection against infant mortality, diarrheal diseases, respiratory infections, allergies, and other conditions, in addition to being a protective factor against maternal breast cancer and promoting better orofacial development in children.^2,3 The National Study on Child Feeding and Nutrition (ENANI) carried out in 2019 showed that, despite Brazil's progress in breastfeeding, less than half of children aged 0 to 6 months were being exclusively breastfed (45.7%)⁴. This data contradicts the global target presented in the 2030 Agenda for Sustainable Development Goals, which proposes to reach at least 50% of EBF in the first 6 months of life by 2025 and 70% by 2030.⁵ In addition, the prevalence of continued breastfeeding in the first year of life (among children aged 12 to 23 months) in the country was 43.6%, with the median duration of EBF being three months, according to ENANI-2019.⁴

There are several factors related to the choice of not breastfeeding or stopping breastfeeding early. Studies suggest that conditions such as previous obesity or overweight, low education level, cesarean section, perception of insufficient breast milk, maternal illness, refusal to breastfeed, return to work or school, infant illness and cultural factors directly influence this decision.^6-8 In addition to the primary role of health care provided to mothers, from prenatal care, delivery, puerperium until the first months of the baby's life, where nursing plays a leading role in care, mainly through education and health promotion in primary health care.⁹ In view of this, it is important to be aware of the social factors that determine the health of infants and mothers. Thus, theorists such as Dahlgren and Whitehead¹⁰ describe the social determinants of health as factors related to the population's living and working conditions that influence its health status. The model described by them is widely used, precisely because it addresses the relationships between social factors and individual and collective health.¹⁰ In addition to this broader understanding of the social determinants of health, in an attempt to understand more deeply the factors that affect breastfeeding, the Lancet Breastfeeding Series Group, based on a systematic review, proposed a conceptual model to identify the components of an environment conducive to breastfeeding, classifying the determinants into three categories: 1) structural; 2) environmental; and 3) individual. This framework provides a theoretical basis for exploring the specific determinants of breastfeeding in different sociocultural contexts.^3,8 Despite the large number of studies on the SDH (Social Determinants of Health) of EBF, few address EBF adherence on the 7^th and 27^th days after birth, which justifies the question of this research: what are the social determinants of health of exclusive breastfeeding on the 7^th and 27^th days after birth? Therefore, it is essential to understand the barriers that EBF faces and to identify the nuances of this process, so that it is possible to outline actions directed to the needs of each population. Thus, this study aims to analyze the social determinants of health of exclusive breastfeeding on the 7^th and 27^th day after delivery.

Methods

Type of study, population, and sample. This is a longitudinal, multicenter study with a quantitative approach that used data from the Viver Project.¹⁰ This study was conducted with postpartum women and newborns in two maternity hospitals in the metropolitan region and in one maternity hospital in the northern region of the state of Espírito Santo, in the southeast of Brazil. The maternity hospitals that participated in the study were selected based on the following aspects: a) those that performed the most deliveries in the region; b) being located in one of the two health regions; c) having a diversity of care, with 80% to 100% coverage by the Unified Health System and 100% private or covered by supplementary health insurance. The population of the Viver Project corresponds to all mothers and children born alive or who died in the perinatal period. They were invited to participate in the study from August 2019 to January 2020, resulting in an initial population of 5,369 mother/baby binomials. The study sample was a census sample, as it included the entire population of mothers of children born in the three maternity hospitals that met the selection criteria, covering the entire universe investigated during the study period.

Techniques and Procedures. To conduct this study, the sample investigated was composed of two moments: 7^th and 27^th days after delivery, including two samples of mother/baby dyads, with 2,325 and 1,819, respectively. With a percentage of losses and refusals of 21.7% (n = 506) between the two periods. To capture the study sample, an interview was initially conducted in the maternity hospital, before hospital discharge. From that moment in question, for this study, sociodemographic and prenatal-related variables were used. The independent variables investigated in the study were: maternal characteristics, at both time points, consisting of age group, marital status, race, maternal years of schooling, maternal employment, family income, socioeconomic status according to the Brazilian Association of Research Companies, which uses the purchasing power of families as a classification criterion, from highest (A) to lowest (E), number of people living in the same household, use of alcohol and/or tobacco and use of illicit drugs. Variables related to breastfeeding: feeding and deleterious oral habits investigated on the 7^th and 27^th days of the babies' lives. Data collection was performed by telephone survey, using a previously prepared research instrument, on the 7^th and 27^th days of the child's life. However, in order to minimize segment losses, a characteristic of this type of study, the first monitoring was carried out between the 7^th and 10^th day after birth and the second between the 27^th and 30^th day, by a team trained for this purpose.

Data analysis. A descriptive analysis of the data was carried out using frequency tables with numbers and percentages. The variables that most influence women in exclusive breastfeeding were assessed by logistic regression. The significance level adopted was 5%. The statistical package IBM SPSS 20 - was used for this analysis.

Ethical aspects. The study was approved by the Human Research Ethics Committee of the University of Vila Velha (CAAE 02503018.0.0000.5064). The Informed Consent Form was signed by the mother or guardian of the child, while still in the maternity ward, and they were instructed that they would be contacted by telephone to continue the research.

Results

In total, 2,325 and 1,819 postpartum women were interviewed on the 7^th and 27^th days, respectively. The predominant age range was between 20 and 34 years, at both times, 69.5% and 68.7%. Of these, the majority lived with a partner, 82.4% and 82.7%, respectively and 48.7% declared themselves to be brown. Regarding years of study, 55.7% and 58.1% studied for 12 years or more, and 53.8% and 56.3% had a job. The predominant family income was up to two minimum wages, representing 45.8% and 44% of the times investigated. It was found that 39% and 40.2% of the study samples belonged to socioeconomic class B and lived with four to six people in the same household, corresponding to 51.9% and 51.7%. There is no statistical significance between the two moments, that is, the samples from the two periods investigated are equivalent (Table 1).

Of the 80.7%, 79.2% remained on EBF on the 7^th day and 27^th day on 79.2%. 19.3% on the 7^th day, and 20.8% received complementary feeding on the 27^th day. Of these, 86% on the 7^th day and 83.4% on the 27^th day were fed with human milk and industrialized formula (Table 2). Regarding difficulty in breastfeeding, 89.1% and 78.2% did not present this difficulty on the 7^th and 27^th days (Table 2). The data focused on deleterious oral habits investigated on the 7^th and 27^th days after birth showed that 79.6% and 73.8%, respectively, did not perform finger sucking. On the 7^th day, 66.9% did not use a pacifier, a practice that decreased to 57.4% on the 27^th day. The non-use of a bottle was characterized by 91% on the 7^th day and 76.1% on the 27^th day (Table 2).

Regarding EBF on the 7^th day and the determinants related to mothers, Table 3 shows a relationship with marital status. Mothers with a partner were more likely to maintain EBF (adjusted OR = 1.86; 95% CI = 1.28-2.72) than those without a partner. In addition, the relationship between EBF and alcohol and/or tobacco consumption and not using illicit drugs was also significant. It was revealed that women who consumed alcohol and/or tobacco and who did not use illicit drugs had 1.82 and 2.99 chances of practicing EBF, respectively (adjusted OR = 1.82; 95% CI = 1.15 - 2.87; adjusted OR = 2.99; 95% CI = 1.24 - 7.17).

The logistic regression between exclusive breastfeeding on the 7^th day and data related to the newborn and care provided during the prenatal period showed that children born with normal weight had 2.52 (adjusted OR = 2.52; 95% CI = 1.48-4.31) chances of practicing EBF than those born with low weight, and mothers who did not have difficulties breastfeeding had 2.701 chances of maintaining EBF than those who had this difficulty (adjusted OR = 2.70; 95% CI = 2.07-3.56) (Table 4).

The age group of the mothers analyzed on the 27^th day after delivery was shown to be a relevant determinant regarding EBF; mothers up to 19 years old were 1.934 times more likely to practice EBF than those aged 20 or older (adjusted OR = 1.93; 95% CI = 1.07-3.49) (Table 5).

Newborns born at term were 2.28 times more likely to practice EBF than those born prematurely (adjusted OR = 2.28; 95% CI = 1.18-4.40). And mothers who reported no difficulty breastfeeding were 8.827 times more likely to maintain EBF on the 27^th day after delivery than those who reported this difficulty (adjusted OR = 8.82; 95% CI = 5.98-13.02) (Table 6).

Discussion

There are many determinants that affect exclusive breastfeeding, influencing the decision-making of nursing mothers about whether or not to continue with this practice. The EBF rate (80.7% and 79.2%) at both times analyzed, 7^th and 27^th day after delivery, was satisfactory. The different pro-breastfeeding approaches that are carried out during prenatal care may have contributed to achieving these results. A study showed that 87% of mothers had six or more prenatal consultations, and a scoping review that analyzed the health determinants of EBF reinforced that prenatal care and the number of consultations carried out during this period are determinants for the success of EBF,^12,13 ​​in addition to the lack of difficulty in breastfeeding (78.2% and 89.1%), present in the periods investigated. This determinant is addressed both during prenatal care and, more intensively, during the postpartum period, mainly through nursing care, in which breasts are assessed and guidance is provided regarding possible changes that may occur at the beginning of breastfeeding and how to deal with them. It is known that no anatomical type of nipple can prevent breastfeeding, although its malformation may make it difficult for the baby to latch on correctly. This difficulty can be overcome through scientific and technical knowledge on the part of the health team, as well as knowledge regarding the lactation process.¹⁴

The marital status of the women studied was a determining factor in EBF on the 7^th day after delivery. Those who had a partner were more likely to maintain EBF on the 7^th day after delivery than those without this support network. This finding corroborates that found in other studies. In Nigeria, when investigating the importance of a support network for exclusive breastfeeding in the first months of an infant's life, it was shown that support from a partner is crucial for the continuation of this practice.¹⁵ This was also significant in a study conducted in China (OR = 1.91) when the father and close friends provided support in the first month after birth⁸. This finding reinforces that the presence of a husband/partner as support for the mother and newborn contributes to the practice and maintenance of exclusive breastfeeding.

The relationship between alcohol and/or tobacco use and EBF on the 7^th day after delivery appeared to be a determinant in this period. As well as not using illicit drugs. It is confirmed that in the second moment, that is, in the perinatal period, the determinant of alcohol and/or tobacco use was not relevant for the analysis. In this context, a study that investigated the outcome of breastfeeding in drug-using mothers on the 7^th, 15^th, and 30^th day after delivery identified a mean EBF of 28.8 days, and mothers who used legal or illegal drugs and continued to be monitored after delivery maintained EBF.¹⁶ The Brazilian Federation of Gynecology and Obstetrics Associations (Febrasgo) and the Ministry of Health contraindicate breastfeeding when the mother is using illegal drugs such as cocaine, heroin, and marijuana, as these and other drugs can pass through the mother's milk and harm the baby, in addition to altering the mother's cognitive behavior, posing a risk to the necessary care for their children.^17,18 The consumption of legal and illegal substances during breastfeeding should be addressed in the context of prenatal and postpartum care, emphasizing the harm this practice causes to the mother/baby binomial. New studies are suggested that can analyze this relationship, alcohol and breastfeeding in more depth in order to explain such causality.

Low birth weight and nipple problems were negatively associated with exclusive breastfeeding in a multicenter study conducted in China.⁶ In the study in question, children born with normal weight were more likely to maintain EBF on the 7^th day after delivery. Therefore, normal birth weight is a positive determinant of EBF, since the opposite, low birth weight, can lead to the early introduction of infant formulas, without acceptable clinical justification. In these cases, it is extremely important to evaluate other conditions, such as correct nipple latch when the baby is breastfeeding, and clinical evaluation of the mother's breasts, among others.¹⁹ Studies have identified that previous successful breastfeeding and knowledge about its benefits are factors that are associated with EBF, unlike the findings of this study, which did not find a relationship between previous experience and EBF.^8,20 However, women who did not have difficulty breastfeeding until the 7^th day after delivery were more likely to maintain EBF.

Regarding EBF on the 27^th day after delivery, maternal age up to 19 years was a significant determinant. A recent study in India, however, showed that maternal age was negatively associated with exclusive breastfeeding.¹⁶ A negative association between maternal age and EBF was also found in another study.⁶ Thus, regarding maternal age, the data are in line with the literature, which highlights that adolescent mothers are more likely to wean early. However, the data found raise important points that may justify this finding, such as the role of an effective support network, from the hospital, family, community and, mainly, primary health care, which welcomes and provides specialized assistance to these adolescent mothers.²⁰

In addition to these factors, gestational age was shown to be crucial for the success of breastfeeding, since children who were born at term were more likely to maintain EBF when compared to those born prematurely (OR = 1.572). This finding is supported by other studies.²¹ The determinant of not having difficulty breastfeeding was a protective factor at both times investigated. This determinant investigated nipple fissures, adequate breastfeeding technique, correct position and latch, among other problems identified by the mothers. Therefore, it is concluded that the mothers were successful in the care provided both during pregnancy and during the postpartum period. Studies have shown that counseling and guidance on breastfeeding are a strong strategy for promoting, protecting, and supporting breastfeeding.⁹ In addition to the role of nursing in this care, being the main professional category that offers support and assistance to mothers at this time.⁹

Among the limitations of the study, we highlight the number of mothers who continued to respond to the telephone survey on the 27^th day after delivery, even with all the strategies to reach these participants, which reduced the sample for the targeted monitoring and the lack of monitoring of the sample investigated until the sixth month of life of the babies, the period suggested for EBF. This was not possible due to problems in contacting the participants of the study, which took place during the COVID-19 pandemic.

Conclusion. The relationship between social determinants of health, such as marital status, maternal lifestyle habits, birth weight of the baby, and difficulties in breastfeeding, influences the practice of EBF. Understanding and comprehending the social determinants of health can favor greater adherence to EBF, in addition to contributing to greater knowledge and improvement of nursing practice in the context of breastfeeding.