Background: Previous studies have demonstrated that adolescent mothers present a higher risk of not breastfeeding or of early interruption of this practice. Considering the scarcity of studies investigating the determining factors of breastfeeding in adolescent mothers, and the absence of studies exploring the determining factors of breastfeeding maintenance for different periods of time in a single population of adolescent mothers, the aim of this research was to identify factors associated with breastfeeding maintenance for at least 6, 12, and 24 months in adolescent mothers. Methods: Data analysis from a randomised control trial involving adolescent mothers recruited at a university hospital in southern Brazil. Participants were followed through the first year of life of their infants and reassessed at 4–7 years. Factors associated with any breastfeeding for at least 6, 12, and 24 months were assessed using multivariate Poisson regression. Results: Data for 228, 237, and 207 mothers were available, respectively. Breastfeeding maintenance for at least 6, 12, and 24 months was observed in 68.4, 47.3, and 31.9% of the sample, respectively. Only one factor was associated with breastfeeding maintenance at all outcomes: infant not using a pacifier showed a higher probability of breastfeeding maintenance in the first 2 years. Maternal grandmother breastfeeding support and exclusive breastfeeding duration were associated with breastfeeding maintenance for 6 and 12 months. The other factors evaluated were associated with breastfeeding maintenance at only one of the time points assessed: 6 months, maternal skin color (black/brown); 12 months, female infant and partner breastfeeding support; and 24 months, older paternal age and multiparity. Conclusions: The present findings shed light upon barriers and facilitators of breastfeeding practices among adolescent mothers. In order to contribute to the challenge of increasing BF duration among adolescent mothers interventions aimed at boosting breastfeeding maintenance among this population should take into consideration the determining factors here identified. Additionally, breastfeeding education and support should be provided continuously as factors influencing these practices vary with time. Thus, support for adolescent mothers during the different stages of breastfeeding need to be tailored to have a positive impact on breastfeeding experience. Keywords: Breastfeeding, Breastfeeding duration, Determinants of breastfeeding, Adolescent, Adolescent behavior, Cohort study * Correspondence: email@example.com Post-Graduate Program in Child and Adolescent Health, Department of Pediatrics, Faculty of Medicine, Rua Ramiro Barcelos, 2400 2º andar, Porto Alegre RS CEP: 90035003, Brazil © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Muelbert and Giugliani BMC Public Health (2018) 18:675 Page 2 of 11 Background when cohabiting. It consisted of six counseling sessions on The positive impact of breastfeeding on child and mater- breastfeeding and healthy complementary feeding, the first nal health, in both the short and long terms, and in both one held at the maternity ward and the subsequent ones developing and developed countries, is widely recog- at the mothers’ homes. The mother-infant dyads were nized . Nevertheless, breastfeeding rates in inter- followed through the first year of life of their infants and national and Brazilian settings are far from reaching reassessed when the children were 4–7 years old. Details optimal levels . In Brazil, the last national survey on on the methodology, intervention, and clinical trial results the prevalence of breastfeeding suggests that breastfeed- can be found elsewhere [11–14]. ing indicators did not advance in the last decade. The The study took place at the maternity ward of the Hos- prevalence of exclusive breastfeeding in infants under pital de Clínicas de Porto Alegre between May 2006 and 6 months and of any breastfeeding in infants under January 2008. Adolescent mothers and their respective in- 24 months has remained unchanged, at about 37 and fants were invited to participate. Maternal grandmothers 52%, respectively. The only indicator showing improve- could also participate whenever they cohabited with the ment was the prevalence of breastfeeding in infants aged mother-infant dyad. The hospital where the study was car- 21 to 23 months, which increased from 23.3% in 2006 to ried out is a Baby Friendly teaching hospital that assists 31.8% in 2013 . primarily users of the Brazilian public health care system Some studies have pointed out that adolescent (approximately 3 thousand deliveries annually). mothers show a lower prevalence of breastfeeding initi- Mothers with the following characteristics were consid- ation and shorter breastfeeding duration [3–5] when ered eligible for the study: age under 20 years, residence in compared with adult mothers; this finding has also been the same municipality where the study took place), having observed in Brazil [6–8]. Considering this scenario, the given birth to healthy singleton newborn weighing 2500 g need to invest in breastfeeding promotion, protection, or more, and having initiated breastfeeding at the mater- and support strategies targeted at younger mothers be- nity ward. Mothers who could not stay in the rooming-in comes evident. It is known that the impact of this type setting due to mother or newborn health problems were of intervention can vary greatly, depending on the char- not included in the study. Also, because the intervention acteristics of the intervention, including the setting involved maternal grandmothers, adolescent mothers res- where it is performed, the agents responsible for deliver- iding with their mothers-in-law (paternal grandmothers) ing it, the type of message conveyed, and number of ex- were not included to avoid a confounding factor. posures to the intervention, among other factors . For the present study, sample size power was calculated Moreover, in order for an intervention to be successful, a posteriori, considering the sample available for analysis. it is necessary to take into consideration the determi- The following parameters were used: breastfeeding preva- nants of early weaning and of breastfeeding maintenance lence of 69.7% at 6 months, 50.1% at 12 months, and in the target population, as these are known to vary and 32.2% at 24 months [12, 15], and a minimum relative risk therefore may be different in adolescent mothers when of 1.25, 1.5, and 1.65, respectively, to assess associations compared with adult mothers . Furthermore, the dif- between the variables and outcomes of interest. The sam- ferent factors associated with breastfeeding practices ple available for assessing the outcome (breastfeeding) at (breastfeeding initiation, exclusiveness and maintenance 6, 12, and 24 months presented a power of at least 80% in for given periods) should be carefully considered as well. the two-tailed hypothesis test, at a significance level of 5%. Considering the scarcity of studies investigating the de- Data collection occurred at different moments. Adoles- termining factors of breastfeeding in adolescent mothers, cent mothers and maternal grandmothers were inter- and the absence of studies exploring the determining fac- viewed separately at the maternity ward. This first tors of breastfeeding maintenance for different periods of interview focused on collecting sociodemographic data, time in a single population of adolescent mothers, the ob- information on prenatal care, delivery and previous ex- jective of this study was to identify the factors associated perience with breastfeeding. Grandmothers answered a with breastfeeding maintenance for at least 6, 12, and different questionnaire. The follow-up questionnaire was 24 months in a cohort of adolescent mothers. applied monthly up to the sixth month of life and every 2 months until they completed 1 year, either by telephone Methods interview or home visit. This questionnaire included ques- This study used data retrieved from the database of a ran- tions related to breastfeeding, complementary feeding, domized clinical trial. The original intervention aimed to sources of breastfeeding support, pacifier use, and bottle increase the prevalence of exclusive breastfeeding and any use. To confirm the quality of the information collected, breastfeeding and to improve complementary feeding 5% of the participants were subjected to a second inter- practices among children of adolescent mothers; the inter- view by the field researcher containing selected questions vention included the children’s maternal grandmothers, from the follow-up questionnaire. Muelbert and Giugliani BMC Public Health (2018) 18:675 Page 3 of 11 When the children were between 4 and 7 years old, adopted, i.e., blocks were hierarchically organized based the participants were contacted once again by telephone, on the proximity of each exposure factor to the out- mail, or social networks; whenever necessary, the fam- come. Therefore, different variables were distributed into ilies were sought at home, at the latest address provided. four blocks. The first block (distal) comprised sociodemo- Once located, participants were requested to visit the graphic variables, maternal and family characteristics; the clinical research center at the hospital. At this occasion, second block (distal intermediate) comprised variables re- data were collected on breastfeeding duration, feeding lated to the prenatal period; the third block (proximal patterns, children’s weight and height, as well as updated intermediate), variables related to labor/delivery, the im- data on the mother, child, and family. mediate postpartum period, and newborn characteristics, For the scope of the present study, we aimed to access if such as birth weight and sex; finally, the fourth block the factors associated with breastfeeding maintenance for (proximal) included characteristics of the breastfeeding 24 month or more would be the same as the factors that mothers and infants, including infant feeding patterns influence breastfeeding maintenance for 12 and 6 months, (Fig. 1). Because this study used data from a randomized thus we applied the same regression model for the differ- clinical trial, the variable intervention was added to the ent time points. Data available were submitted to a regres- proximal block of the model to rule out any eventual sion model in order to determine the factors associated interference of the intervention on the results. with breastfeeding maintenance for at least 6 months, at First, analyses were conducted to assess the possibility least 12 months, and at least 24 months. World Health of multi-collinearity and to assess the association be- Organization definition for breastfeeding was used in the tween the outcome and variables of interest in each present study for the three outcomes assessed and there- block, using univariate Poisson regression. Variables in fore breastfeeding maintenance refers to children that re- the first block (distal) that reached a level of significance ceived breastmilk (including expressed or donor milk), of p < 0.20 in the univariate analysis were subjected to regardless of whether they were receiving other foods and multivariate Poisson regression (intrablock analysis). liquids including non-human milk and formula . Any variables reaching a significance level of p <0.10 in A regression model with a hierarchical approach was the multivariate analysis remained in the model for adjust- developed in which variables were distributed in blocks ment of the next block. Subsequently, variables in the sec- according to their relationship with the outcome . ond block (distal intermediate) that reached p <0.20 in The approach suggested by Boccolini et al. was the univariate analysis were subjected to multivariate Fig. 1 Hierarchical model used to identify factors associated with breastfeeding maintenance in adolescent mothers. * Variable included in the model at 12 and 24 months only Muelbert and Giugliani BMC Public Health (2018) 18:675 Page 4 of 11 Poisson regression along with the variables from the distal Breastfeeding maintenance for at least 6 months was ob- block that reached p < 0.10 in the previous multivariate served in 68.4% of the sample, and for at least 12 and analysis; and so on. This model predicted that, once a vari- 24 months, in 47.3 and 31.9% of the mothers, respectively. able reached p < 0.10 in intrablock analysis, it would re- Table 1 shows the results of the multivariate analysis main in the model until the end, adjusting associations of associations between breastfeeding maintenance for at between variables from the other blocks due to their least 6 months and the variables selected, included in possible role as confounding factors. The level of as- the model in blocks, as described above. Significant as- sociation between the different variables and the out- sociations were observed between the outcome and ma- come was estimated using crude relative risk (RRc) ternal skin color (black/brown), maternal grandmother and adjusted relative risk (RRa) and respective 95% support of breastfeeding, never having used a pacifier, confidence intervals (95% CI); associations were con- and longer exclusive breastfeeding duration (0.4% for sidered significant when p < 0.05. Missing data were each day of exclusive breastfeeding). Only one variable managed as listwise deletion as regression model al- from the distal block and none from the two intermedi- lows only entire records to enter the model for ana- ate blocks were associated with the outcome. lysis. Statistical analyses were conducted using the In relation to the factors associated with breastfeeding Statistical Package for the Social Sciences version 21.0 maintenance for at least 12 months (Table 2), none of (IBM Corp., 2012). the variables from the distal and distal intermediate The present study was conducted according to the blocks showed significant associations with the outcome. guidelines established by Resolution no. 466/2012 of the Of the five variables showing significant associations, four National Health Council, from the Brazilian Ministry of were from the proximal block – maternal grandmother Health. Mothers and grandmothers received detailed in- and partner support of breastfeeding, never having used a formation on the study and signed an informed consent pacifier, and longer exclusive breastfeeding duration (0.2% form prior to any study procedures, and again before the for each day of exclusive breastfeeding) – and one was last assessment. For adolescents under 18 years of age, from the proximal intermediate block – infant female sex. consent was obtained from the adolescent mother and a Finally, of the three variables associated with breast- parent/guardian. This research obtained approval from feeding maintenance for at least 24 months (Table 3), the Research Ethics Committee of Hospital de Clínicas two were from the distal block – paternal age ≥ 22 years de Porto Alegre (protocol no. 120249). The clinical trial and multiparity – and one was from the proximal block was registered at ClinicalTrials.gov (NCT00910377). – never having used a pacifier. Table 4 presents the variables that showed association with at least one of the three outcomes assessed. Of the Results eight variables, five were associated with only one of the A total of 323 adolescent mothers initiated the study, three outcomes, two with two outcomes – maternal 257 (80%) participated in the 6th month follow-up, 237 grandmother support of breastfeeding and exclusive (73%) remained up to 12 months, and 207 (64%) were breastfeeding duration –, and only one variable was as- available for the final evaluation (4–7 years). There was sociated with all three outcomes – infant never having no statistically significant difference for maternal charac- used a pacifier. teristics (skin color, age, educational level, number of prenatal visits, and number of children) and children’s Discussion characteristics (gender, birth weight, and mode of deliv- This is the first study to investigate factors associated ery) between those who completed the study and the with breastfeeding maintenance for 24 months in adoles- participants who were lost to follow-up. cent mothers and also for different periods of time in After exclusion of the cases lost to follow-up and this population. The demonstration that the factors asso- participants with missing records, data from 228, 237, ciated with breastfeeding maintenance may vary depend- and 207 mothers were available for analysis of the ing on the time frame assessed and that they show factors associated with breastfeeding maintenance for peculiarities in adolescent mothers adds new and rele- at least 6, 12, and 24 months, respectively. vant information to the existing state of the art. Maternal age at the beginning of the study ranged We identified only two previous studies that also in- from 13 to 19 years, with a mean of 18 years; most vestigated factors associated with breastfeeding mainten- mothers (52.9%) had at least 8 years of formal educa- ance for 6, 12, and 24 months – one conducted in tion, had a partner (84%) and cohabited with the in- Croatia  and the other in the United States . fant’s father (62%); half of the adolescent mothers Both studies included women of all age groups and also lived with the infant’s maternal grandmother. Mean observed changes in the factors associated with breastfeed- paternal age was 22 years. ing maintenance over time. However, of the determining Muelbert and Giugliani BMC Public Health (2018) 18:675 Page 5 of 11 Table 1 Factors associated with breastfeeding maintenance at 6 months in adolescent mothers. Analysis of variables subjected to Poisson hierarchical regression analysis Distal block (n = 228) N (%) RRc (95%CI) RRa (95%CI) Maternal age ≥18 years 124 (54.4) 1.17 (0.98–1.41) 1.15 (0.96–1.38) Paternal age ≥22 years 111 (48.6) 1.11 (0.95–1.33) – Maternal education ≥8 years 123 (53.9) 0.92 (0.77–1.10) – Maternal skin color * * Black/brown 89 (39.0) 1.21 (1.02–1.43) 1.22 (1.03–1.44) Parity Multiparous 33 (14.5) 0.97 (0.75–1.26) – Cohabitation with partner at beginning of study 135 (59.2) 1.13 (0.94–1.36) 1.07 (0.87–1.38) Cohabitation with maternal grandmother at beginning of study 123 (53.9) 0.83 (0.70–0.99) 0.87 (0.71–1.06) Distal intermediate block Planned pregnancy 60 (26.3) 0.93 (0.76–1.15) – Smoked during pregnancy Did not smoke 150 (65.8) 1.14 (0.93–1.38) – Number of prenatal visits ≥7 visits 144 (63.1) 1.18 (0.96–1.44) 1.17 (0.95–1.43) Received prenatal guidance on breastfeeding 89 (39) 1.00 (0.84–1.20) – Participated in prenatal classes/groups 49 (21.5) 1.10 (0.90–1.33) – Proximal intermediate block Type of delivery Vaginal 179 (78.5) 0.98 (0.79–1.21) - Infant sex Female 112 (49.1) 1.09 (0.92–1.31) - Birth weight ≥3200 g 110 (48.2) 0.99 (0.83–1.18) - Intention to breastfeed ≥6 months 218 (95.6) 1.38 (0.74–2.59) - Proximal block Exposed to intervention 115 (50.4) 1.15 (0.96–1.37) 1.00 (0.86–1.18) * * Maternal grandmother supports breastfeeding 163 (71.4) 1.44 (1.08–1.93) 1.31 (1.04–1.64) Partner supports breastfeeding 164 (71.9) 1.48 (1.10–1.99) 1.27 (0.99–1.63) Pacifier use ** ** Does not use 102 (44.7) 1.73 (1.44–2.07) 1.53 (1.30–1.80) a ** ** Exclusive breastfeeding duration (days) 89 (39–180) 1.005 (1.004–1.007) 1.004 (1.002–1.005) * ** p < 0.05; p < 0.001 Median (25th–75th interquartile range) RRc crude relative risk, RRa adjusted relative risk, 95%CI 95% confidence interval factors assessed by Langellier et al. in the United States, the Croatian study by Zakarija-Grkovic et al. (antenatal four (intention to breastfeed prior to birth, breastfeeding at course attendance). In our study, not using a pacifier was the maternity ward, being interviewed in Spanish, and the only factor associated with breastfeeding maintenance mother not returning to work in the first 3 months) were at the three time points assessed. positively associated with breastfeeding maintenance at the The association between pacifier use and duration of three time points assessed, compared to only one factor in both exclusive breastfeeding and any breastfeeding has Muelbert and Giugliani BMC Public Health (2018) 18:675 Page 6 of 11 Table 2 Factors associated with breastfeeding maintenance at 12 months in adolescent mothers. Analysis of variables subjected to Poisson hierarchical regression analysis Distal block (n = 237) N (%) RRc (95% CI) RRa (95% CI) Maternal age ≥18 years 133 (56.1) 1.08 (0.82–1.42) - Paternal age ≥22 years 117 (49.3) 1.05 (0.80–1.37) - Maternal education ≥8 years 135 (56.9) 0.90 (0.69–1.18) - Maternal skin color Black/brown 84 (35.4) 1.22 (0.94–1.60) - Parity Multiparous 35 (14.7) 1.10 (0.77–1.57) - Cohabitation with partner at beginning of study 145 (61.2) 1.06 (0.8–1.40) - Cohabitation with maternal grandmother at beginning of study 132 (55.7) 0.89 (0.68–1.16) - Distal intermediate block Planned pregnancy 62 (26.1) 0.81 (0.58–1.14) – Smoked during pregnancy Did not smoke 163 (68.7) 1.30 (0.94–1.79) – Number of prenatal visits ≥7 visits 153 (64.5) 1.00 (0.76–1.33) - Received prenatal guidance on breastfeeding 100 (42.2) 1.07 (0.81–1.40) – Participated in prenatal classes/groups 52 (21.9) 1.13 (0.83–1.53) – Proximal intermediate block Type of delivery Vaginal 186 (78.5) 0.86 (0.64–1.17) - Infant sex Female 117 (49.3) 1.31 (0.99–1.72) 1.32 (1.003–1.73) Birth weight ≥3200 g 123 (51.9) 1.07 (0.82–1.40) - Intention to breastfeed ≥12 months 190 (80.1) 1.29 (0.87–1.91) 1.31 (0.88–1.96) Proximal block Exposed to intervention 111 (46.8) 0.73 (0.55–0.97) 0.98 (0.78–1.23) Mother worked/studied in the first year of life 34 (14.3) 1.30 (0.82–2.06) – ** * Maternal grandmother supports breastfeeding 115 (48.5) 4.99 (2.98–8.37) 2.14 (1.22–3.77) ** * Partner supports breastfeeding 113 (47.6) 4.06 (2.56–6.45) 1.63 (1.06–2.53) Pacifier use ** ** Does not use 98 (41.3) 3.15 (2.29–4.33) 2.17 (1.55–3.03) a ** * Exclusive breastfeeding duration (days) 89 (39–189) 1.007 (1.005–1.009) 1.002 (1.00–1.004) * ** p < 0.05; p < 0.001 Median (25th–75th interquartile range) RRc crude relative risk, RRa adjusted relative risk, 95%CI 95% confidence interval been widely investigated, with evidence suggesting that mothers, aged 18–19 years, the use of pacifier was posi- pacifier use can have negative effects on breastfeeding tively associated with breastfeeding practice at 1 week but duration [21, 22]. In contrast, recent research with this association was inverse among older mothers aged 30 American mothers has demonstrated that among young or more . However, no effect on breastfeeding Muelbert and Giugliani BMC Public Health (2018) 18:675 Page 7 of 11 Table 3 Factors associated with breastfeeding maintenance at 24 months in adolescent mothers. Analysis of variables subjected to Poisson hierarchical regression analysis Distal block (n = 207) N (%) RRc (95%CI) RRa (95%CI) Maternal age ≥18 years 116 (56.0) 1.21 (0.80–1.82) - Paternal age * * ≥22 years 99 (47.8) 1.66 (1.10–2.51) 1.59 (1.06–2.40) Maternal education ≥8 years 110 (53.1) 1.36 (0. 90–2.05) 1.32 (0.88–1.99) Maternal skin color Black/brown 78 (37.7) 1.22 (0.82–1.82) - Parity * * Multiparous 30 (14.5) 1.73 (1.13–2.66) 1.79 (1.17–2.74) Cohabitation with partner at beginning of study 125 (60.4) 1.15 (0.76–1.74) - Cohabitation with maternal grandmother at beginning of study 109 (52.6) 0.95 (0.64–1.42) - Distal intermediate block Planned pregnancy 49 (23.6) 1.55 (0.88–2.72) 1.45 (0.84–2.51) Smoked during pregnancy Did not smoke 140 (67.6) 1.50 (0.92–2.42) 1.47 (0.93–2.34) Number of prenatal visits ≥7 visits 134 (64.7) 0.99 (0.65–1.51) - Received prenatal guidance on breastfeeding 82 (39.6) 0.99 (0.66–1.49) – Participated in prenatal classes/groups 46 (22.2) 1.21 (0.78–1.89) – Proximal intermediate block Type of delivery Vaginal 154 (74.4) 1.07 (0.67–1.72) - Infant sex Female 106 (51.2) 1.22 (0.81–1.82) – Birth weight ≥3200 g 98 (47.3) 0.82 (0.55–1.23) – Intention to breastfeed ≥24 months 135 (65.2) 1.23 (0.79–1.90) - Proximal block Exposed to intervention 98 (47.3) 0.87 (0.58–1.30) – Mother worked/studied in the first year of life 48 (23.2) 1.36 (0.79–2.32) – ** Maternal grandmother supports breastfeeding 61 (29.4) 6.34 (3.17–12.68) 3.33 (0.79–13.92) ** Partner supports breastfeeding 60 (29.5) 6.52 (3.27–13.03) 1.79 (0.49–6.52) Pacifier use ** * Does not use 98 (47.3) 4.13 (2.45–6.97) 2.05 (1.07–3.92) a ** Exclusive breastfeeding duration (days) 59 (29–119) 1.006 (1.003–1.010) 1.0 (0.996–1.004) * ** p < 0.05; p < 0.001 Median (25th–75th interquartile range) RRc crude relative risk, RRa adjusted relative risk, 95%CI 95% confidence interval maintenance was assessed limiting comparisons with the demonstrate a negative association between pacifier use present study. Thus, the mechanisms underlying this asso- and breastfeeding maintenance in adolescent mothers in ciation are not fully understood and could be affected by Brazil: infant not using a pacifier in our population in- maternal age. In this sense, our study was the first to creased the chance of maintaining breastfeeding for at Muelbert and Giugliani BMC Public Health (2018) 18:675 Page 8 of 11 Table 4 Variables associated with breastfeeding maintenance in but not for 6 or 24 months. Even though there is consen- adolescent mothers sus in the literature on the importance for breastfeeding of Breastfeeding Breastfeeding Breastfeeding the support provided by the infant’s father, some studies ≥6 months ≥12 months ≥24 months have suggested that fathers are not always prepared to pro- Distal block vide this support. For instance, a Brazilian study involving Paternal age, X adolescent mothers found a 1.6 higher risk of breastfeeding ≥22 years interruption before 6 months when the adolescent mother Maternal skin color, X was married ; another study, also conducted in Brazil, black/brown identified cohabitation with partner as a risk factor for Multiparity X breastfeeding maintenance for at least 24 months in Proximal women from all age groups . Moreover, experiencing intermediate block partner violence was an important risk factor for breast- Infant sex, female X feeding interruption before 6 months in a study carried out with adolescent mothers in the United States . Proximal block Another partner characteristic that showed a positive Maternal grandmotherXX supports breastfeeding association with breastfeeding maintenance in our study was paternal age, however only at 24 months. To the au- Partner supports X breastfeeding thors’ knowledge, this was the first study investigating factors associated with breastfeeding using multivariate Pacifier use, never X X X analysis that identified an association between paternal Longer exclusive XX breastfeeding duration age and breastfeeding duration. Even though maternal age is among the factors most widely studied, paternal least 6 months by 1.5 and doubled the chance of breast- age tends to be neglected. More studies are needed that feeding maintenance for at least 12 or 24 months. investigate this association in women of all age groups, It is worth to mention that even though pacifier use to clarify the factors involved. It is possible that younger might be indicated to reduce incidence of Sudden Unex- paternal age is related with lower paternal interest in pected Deaths in Infancy (SUDI) and Sudden Infant Death caring for the infant, and also with poor knowledge of Syndrome (SIDS) when given at naptime or bedtime in the positive effects of prolonged breastfeeding on both some countries, the American Academy of Pediatrics and infant and maternal health, especially among teenage other policy makers in Canada, United Kingdom, New couples. Finally, it is also likely that younger fathers see Zealand and Australia recognize that the introduction of breastfeeding as a barrier to resuming full sexual activity pacifiers should be delayed until 4 to 6 weeks to avoid after the infant’s birth, a fact that may be interpreted dif- interference with establishment of breastfeeding. Breast- ferently by older fathers. It is interesting to observe that, feeding is associated with reduced risk of SUDI and SIDS, among the few studies that have explored paternal age however the mechanism behind the protective effects of as a possible risk factor for breastfeeding, all failed to pacifiers on prevention of SUDI and SIDS remain unclear identify a significant association [34–36]; however, none and therefore the indication for the use of pacifier merits of them had adolescent mothers as the target popula- caution to prevent a negative impact on the establishment tion. This finding underscores the relevance of including of breastfeeding [24–28]. the infant’s father or mother’s partner in breastfeeding Maternal grandmother support of breastfeeding showed promotion strategies. a significant association with breastfeeding maintenance In addition to paternal age, another factor that for at least 6 and 12 months, but not for 24 months, des- showed association with breastfeeding maintenance at pite the magnitude of the association. This finding is not 24 months only was the mother having an older surprising, as receiving breastfeeding support from differ- child. There have been reports of positive associations ent sources – especially from the adolescent mother’s between multiparity and exclusive breastfeeding in ad- mother – is known to foster the practice [29, 30]. A recent olescents , but none of the two studies that systematic review demonstrated that the opinion of the in- assessed this variable in adolescent mothers confirmed fant’s maternal grandmother regarding breastfeeding influ- the association between any breastfeeding duration ences maternal decisions: when positive, it may increase and multiparity [10, 33]. Theexperienceacquired by 12% the likelihood of the mother initiating breastfeed- with older children may help the mother overcome ing; when negative, it may reduce by 70% the likelihood of any difficulties during pregnancy, delivery, puerper- breastfeeding . ium, and also during breastfeeding [37, 38]. Studies Partner breastfeeding support was also positively associ- indicate that mothers who had a positive experience ated with breastfeeding maintenance for at least 12 months, with breastfeeding are more likely to breastfeed their Muelbert and Giugliani BMC Public Health (2018) 18:675 Page 9 of 11 subsequent child [39–42], suggesting that effort should be frames. However, looking at the results of a study con- made to support first-time mothers’ with breastfeeding as ducted by the same group of authors with women of all it might have positive impact on subsequent pregnancies ages, selected at the same hospital, and employing similar and breastfeeding practices. Furthermore, women who methodology could be useful to compare factors associ- have experienced motherhood before may have an in- ated with breastfeeding maintenance for at least creased knowledge of infant care, introducing comple- 24 months. In that study, five variables were positively as- mentary feeding at a more appropriate time and sociated with the outcome: not cohabiting with the infant’s maintaining breastfeeding for longer . father, mother staying at home in the first semester after In addition to maternal grandmother support of birth, not using a pacifier, postponed introduction of breastfeeding, another factor positively associated with water, tea, and complementary feeding . Therefore, breastfeeding maintenance for two of the three time pe- the only factor common to both studies was not using a riods assessed, namely 6 and 12 months, was exclusive pacifier. Parity was associated with breastfeeding mainten- breastfeeding duration. This association has been de- ance for at least 24 months among adolescent mothers scribed previously in American adolescents: having ex- only, and paternal age was not explored in that study. clusively breastfed reduced by almost 40% the risk of Some limitations of this study should be addressed. interrupting breastfeeding before 6 months in that popu- For example, the fact that this analysis relied on data ob- lation . A similar finding was observed in another tained from a randomized clinical trial can be considered study, comprising women of all ages: the introduction of as a possible disadvantage. To minimize this limitation, formula during the infant’s first month of life doubled we added the variable intervention to the proximal block the risk of interrupting breastfeeding before 12 months of the regression model, in order to ensure that the asso- . The association between introduction of comple- ciations observed were independent of group allocation mentary feeding to the breastfed infant and shorter in the original trial. Moreover, because the information breastfeeding duration is biologically plausible: first, on breastfeeding for at least 24 months was collected 4 there is a decrease in milk supply as the infant starts to to 7 years after birth, there is a possibility of memory breastfeed less often – a natural phenomenon when they bias. Nonetheless, we believe that this type of bias is un- start to receive other foods ; second, nipple confu- likely as breastfeeding duration was expressed using two sion may occur, as bottles are usually the primary vehicle distinct time frames (< 24 months or ≥ 24 months), and for the intake of water, tea, juices, and other milks at this the time elapsed after the outcome varied from 2 to age . Furthermore, it is possible that the women who 5 years, at the most. Another limitation of the study is the are committed to exclusively breastfeed their babies for attrition rate faced during the follow-up phase common longer are also the ones who will more rigorously ob- to studies that require tracking down participants for serve breastfeeding duration recommendations. follow-up assessments. Even though active search for find- Finally, two other factors contributed to breastfeeding ing participants did not lead to fewer losses, this limitation maintenance in adolescent mothers: maternal skin color did not affect the present findings as the characteristics of (black/brown) and female infant sex. These characteris- participants did not differed between those who com- tics have been previously identified as protective factors pleted the study and those lost during follow-up. for breastfeeding in the Brazilian population [15, 47, 48] where black and brown skin colors are a reflection of Conclusion ethnicity. Nevertheless, this is the first time these find- The factors that influence breastfeeding duration modify ings are described in adolescent mothers that choose to as lactation evolves. Adolescent mothers face many chal- breastfeed, as the two previous studies involving adoles- lenges during their motherhood experience that appear cent mothers failed to find associations between breast- to change as the child grows older and she returns to so- feeding and skin color/race  or infant sex . It is cial and work activities. We believe that the results of interesting to observe that these two factors are closely this study can contribute to the challenge of increasing related to social and cultural disparities, and therefore breastfeeding duration by individual-centered approach vary greatly across populations. In some countries, black , i.e., by taking into consideration the associated fac- women breastfeed for shorter periods than their white tors here identified during planning and implementation counterparts – e.g., in the United States ; in others, of strategies targeted at adolescent mothers. In such male infants tend to be privileged with regard to breast- strategies, it would be important to address the following feeding – e.g., in Timor-Leste . topics: information on pacifier use, providing breastfeed- Our study included adolescent mothers only, and ing education before birth to both expecting mothers therefore it is not possible to compare the factors associ- and family members; the importance of breastfeeding ated with breastfeeding duration in our population with support from the mother’s partner and close family the findings reported for adult mothers at the same time members, especially the infant’s grandmothers, including Muelbert and Giugliani BMC Public Health (2018) 18:675 Page 10 of 11 these subjects in the interventions whenever possible 2. Boccolini CS, Boccolini PDMM, Monteiro FR, Venâncio SI, Giugliani ERJ. Breastfeeding indicators trends in Brazil for three decades. Rev Saude (especially younger fathers); and the importance of ex- Publica. 2017;51:108. https://doi.org/10.11606/S1518-8787.2017051000029. clusive breastfeeding in the first 6 months of life of the 3. American Academy of Pediatrics. Breastfeeding and the use of human milk. infant. Additionally, we recommend that breastfeeding Pediatrics. 2012;129:e827–41. https://doi.org/10.1542/peds.2011-3552. 4. Apostolakis-Kyrus K, Valentine C, Defranco E. Factors associated with education and support should be provided continuously, breastfeeding initiation in adolescent mothers. J Pediatr. 2013;163:1489–94. prenatally and beyond, as we have identified that the fac- https://doi.org/10.1016/j.jpeds.2013.06.027. tors influencing this practices changes with time and 5. Monteiro JCS, Dias FA, Stefanello J, Reis MCG, Nakano AMS, Gomes-Sponholz FA. Breast feeding among Brazilian adolescents: practice and needs. Midwifery. with the expected duration of breastfeeding practices. It 2014;30:359–63. https://doi.org/10.1016/j.midw.2013.03.008. is also necessary to bear in mind that our study has 6. da Cruz MCC, de Almeida JAG, Engstrom EM. Práticas alimentares no identified that white and primiparous mothers tend to primeiro ano de vida de filhos de adolescentes. Rev Nutr. 2010;23:201–10. https://doi.org/10.1590/S1415-52732010000200003. breastfeed for shorter periods of time and more atten- 7. Gusmão AM, Béria JU, Gigante LP, Leal AF, Schermann LB. Prevalência de tion should be given to them when designing strategies aleitamento materno exclusivo e fatores associados : estudo transversal to improve breastfeeding practices. Moreover, we have com mães adolescentes de 14 a 16 anos em Porto Alegre, RS, Brasil. Cien Saude Colet. 2013;18:3357–68. identified that the factors associated with breastfeeding 8. Maranhão TA, Gomes KRO, Nunes LB, de Moura LNB. Fatores associados ao maintenance change over time, which means giving aleitamento materno exclusivo entre mães adolescentes. Cad Saúde more emphasis on one or another factor, depending on Coletiva. 2015;23:132–9. https://doi.org/10.1590/1414-462X201500020072. 9. Sinha B, Chowdhury R, Sankar MJ, Martines J, Taneja S, Mazumder S, the stage of breastfeeding being assessed. All in all, we et al. Interventions to improve breastfeeding outcomes: a systematic expect that these findings will contribute to improve the review and meta-analysis. Acta Paediatr. 2015;104 Suppl 467:114–35. knowledge of aspects still little explored of the determi- https://doi.org/10.1111/apa.13127. 10. Frota DAL, Marcopito LF. Amamentação entre mães adolescentes e não nants of breastfeeding among younger mothers. adolescentes, Montes Claros, MG [Breastfeeding among teenage and adult mothers in Brazil]. Rev Saude Publica. 2004;38:85–92. https://doi.org/10.1590/ Funding S0034-89102004000100012. This study was funded by Conselho Nacional de Desenvolvimento Científico 11. Nunes LM, Giugliani ERJ, do Espírito Santo LC, de Oliveira LD. Reduction of e Tecnológico (CNPq) and Fundo de Incentivo à Pesquisa e Eventos – unnecessary intake of water and herbal teas on breast-fed infants: a randomized Hospital de Clínicas de Porto Alegre (FIPE-HCPA). The funding bodies did not clinical trial with adolescent mothers and grandmothers. J Adolesc Health. 2011; have any role in study design, in the collection, analysis, and interpretation 49:258–64. https://doi.org/10.1016/j.jadohealth.2010.12.009. of data, in the writing of the manuscript, or in the decision to submit the 12. da Silva CF, Nunes LM, Schwartz R, Giugliani ERJ. Effect of a pro- manuscript for publication. breastfeeding intervention on the maintenance of breastfeeding for 2 years or more: randomized clinical trial with adolescent mothers and Availability of data and materials grandmothers. BMC Pregnancy Childbirth. 2016;16:97. https://doi.org/10. The datasets used and/or analysed during the current study are available 1186/s12884-016-0878-z. from the corresponding author on reasonable request. 13. de Oliveira LD, Giugliani ERJ, Santo LC do E, Nunes LM. Impact of a strategy to prevent the introduction of non-breast milk and complementary foods Authors’ contributions during the first 6months of life: a randomized clinical trial with adolescent MM performed data analysis and interpretation, and drafted the manuscript. mothers and grandmothers. Early Hum Dev. 2012;88:357–61. ERJG made substantial contributions to study conception and design, 14. de Oliveira LD, Giugliani ERJ, do Espírito Santo LC, Nunes LM. Counselling supervised the fieldwork, and critically revised the text for intellectual content. sessions increased duration of exclusive breastfeeding: a randomized clinical Both authors have approved the final version submitted for publication. trial with adolescent mothers and grandmothers. Nutr J. 2014;13:73. https:// doi.org/10.1186/1475-2891-13-73. Ethics approval and consent to participate 15. Ministério da Saúde. II research of breastfeeding predominance in Brazilian The present study was conducted according to the guidelines established by capitals and Federal District. Brasília; 2009. http://bvsms.saude.gov.br/bvs/ Resolution no. 466/2012 of the National Health Council, from the Brazilian publicacoes/pesquisa_prevalencia_aleitamento_materno.pdf Ministry of Health. This research obtained approval from the Research Ethics 16. World Health Organization. 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