Introduction

Breast milk is an essential, free, and readily available nutrient for infants with various benefits [1]. For example, exclusive breastfeeding (EBF) for the first 6 months prevents infection-related infant mortality and morbidity [2, 3], and also, EBF and partial breastfeeding reduces the risk of childhood obesity, and being overweight [4, 5]. Similarly, for maternal health, EBF and partial breastfeeding can reduce the risk of postpartum depression [6, 7], breast cancer [3], ovarian cancer, and type 2 diabetes [8, 9].

Based on these multiple benefits, EBF for the first 6 months of life is recommended by the World Health Organisation (WHO) and the United Nations Children’s Fund (UNICEF) [1]. The global target for EBF is to achieve EBF in at least 50% of children in their first 6 months of life by 2025 [10]. The latest statistics show that 48% of children aged < 6 months were exclusively breastfed globally in 2023, a 10% point increase from 2013 [11]. A study of 113 countries revealed that the EBF rate of < 6 months increased in low- and middle-income countries (LMICs) from 2000 to 2019. Its rate was higher in low-income countries (51.2%) than that in middle-income countries, whereas those in high-income countries (HICs) were not reported due to unavailable data [12]. Another study reported in 2021 that the EBF rate of < 6 months was 18% (0.1–57%) in 30 HICs; however, EBF rates in the remaining 21 HICs covered by this study were not estimated due to unavailable data [13].

The Japanese breastfeeding situation is unique because national policies and clinical practices may not follow global recommendations. For instance, the Breastfeeding and Weaning Support Guide issued by the Japanese government emphasises that healthcare professionals should offer appropriate support, including the use of formula milk when necessary, rather than relying solely on breast milk [14]. The guide does not provide clear guidance on EBF during hospitalisation after delivery [14]. The guide also recommends initiating weaning between 5 and 6 months of age, which is earlier than the WHO recommendations [1, 14]. Only 66 of 1,945 (3.4%) obstetric hospitals and clinics in Japan were accredited as Baby Friendly Hospitals (BFHs) that promote EBF in 2021, implying that breastfeeding support in obstetric hospitals and clinics may vary [15–17].

Furthermore, women are hospitalised for an average of 5 d (for singleton vaginal delivery) after delivery in Japan [18, 19]. This is longer than those in Organisation for Economic Co-operation and Development countries (average 1.4–4.4 d) or LMICs (0.5–6.2 d) [20, 21]. Long periods of hospitalisation may increase the opportunity for women to receive tailored breastfeeding support from healthcare professionals. For example, a previous study reported that early initiation of breastfeeding, early skin-to-skin contact, and rooming-in are associated with the continuation of EBF [22]. However, women commonly encounter challenges in breastfeeding practices during the first month, such as the baby’s failure to latch on, sore nipples, maternal feelings of insufficient milk supply, pain, and fatigue [23–25]. Milk supplementation may be used as an option to respond to these challenges. Previous studies conducted in Hong Kong, Vietnam, and the United States have reported that formula milk supplementation is associated with the early cessation of EBF [26–28] and failure to achieve the duration desired by women [29]. However, to our knowledge, no study has examined whether breastfeeding practices during hospitalisation are associated with subsequent practices after discharge in Japan.

Additionally, after discharge from the hospital until 5–6 months postpartum, there are significant changes in the mother’s health, daily life patterns, and the child’s growth. This may affect breastfeeding practices from month to month. Therefore, to better understand appropriate and timely breastfeeding support during and after hospitalisation, a study examining the association between breastfeeding status during hospitalisation and subsequent practice, considering changes in practice patterns over time, is required.

This study had two objectives. First, we aimed to examine the association between EBF during the first 7 d after birth (a proxy for the duration of hospitalisation) and EBF 24-h before the survey among children aged < 6 months and assess the strength of this association by comparing it with the association of EBF during the first day after birth. We also aimed to describe the changes in breastfeeding patterns from the first to the sixth month postpartum based on breastfeeding status during hospitalisation.

Materials and methods

Study design and population

This study was part of the Japan COVID-19 Society Internet Survey (JACSIS), a cross-sectional nationwide internet survey. JACSIS comprises three components: surveys of the general population, women, and male partners. The study participants for each survey were selected from the pooled panels of Rakuten Insight, Inc., an online research company with over 2.2 million panellists enrolled as of 2019 [30]. This study used data from a survey of women. The study population for the women’s survey was pregnant women who were expected to deliver by December 2021 and postpartum women who had a live singleton delivery between January 2019 and August 2021. A sample size estimation was not performed before the survey because the project aimed to examine multiple health and social topics associated with COVID-19. Therefore, we recruited the maximum number of eligible women from the pooled panel. During the recruitment process, a screening survey was conducted to identify 14,086 eligible women (11,661 postpartum and 2,425 pregnant women). Thereafter, they received email invitations to participate in the survey. Subsequently, 8,047 women (6,256 postpartum and 1,791 pregnant women) provided consent to participate in the survey between 28 July and 30 August 2021.

The following criteria were set for data analysis. The inclusion criterion was < 6 months postpartum. The exclusion criteria were as follows: 1) giving contradictory answers, 2) inability to breastfeed for medical reasons, and 3) preterm births before 37 weeks. This criterion was because women with preterm births were most likely to have difficulty practising EBF due to their children’s admission to the neonatal intensive care unit and their immaturity. Based on these criteria, of 6,256 postpartum women, 570 who gave contradictory answers and 4,253 who met the exclusion criteria of 2) or 3) were excluded. Overall, 1,433 postpartum women were included in the analysis (Fig 1). We evaluated whether the distribution of the participating women by prefecture of residence was almost equal to the distribution of births by prefecture in 2020 [31].

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Fig 1. Flow diagram of the recruitment of study participants.

https://doi.org/10.1371/journal.pone.0310967.g001

Statistical analysis

First, we conducted a chi-square test and t-test to assess the distribution of participant characteristics based on their breastfeeding status during the first day and the first 7 d after birth, respectively.

Second, multivariate Poisson regression was performed to analyse the association of first-day EBF and 7-d EBF, with 24-h recall EBF before the survey. The strengths of the association were compared based on the prevalence ratio values. Poisson regression was employed because the prevalence of the outcome exceeded 10% [36].

Finally, we calculated the proportion of 24-h recall breastfeeding practices per age group under 6 months and described the results using area graphs (Figs 2 and 3). Fig 2 illustrates the breastfeeding status with and without exclusive breastfeeding during the first day after birth. Fig 3 shows the breastfeeding status with and without exclusive breastfeeding during the first 7 d after birth. The WHO and UNICEF recommend the area graph as part of the IYCF indicators for children aged 0–23 months, which can show the monthly trends of feeding practices [32]. WHO and UNICEF classify feeding practices into six patterns and plot the feeding status at 2-month intervals in children aged < 6 months; however, our study had to modify the six feeding patterns to five due to data limitations. These patterns were 1) breast milk only, 2) breast milk and non-milk liquids, 3) breast milk and formula milk, 4) breast milk and solid, semisolid, and soft foods, and 5) not breastfed. Additionally, we plotted feeding on a monthly basis to capture the Japanese patterns. We used statistical software, Stata version 15.0, for data analysis. Statistical significance was set at P < 0.05.

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Fig 2. Area graph of breastfeeding status with and without exclusive breastfeeding during the first day after birth.

https://doi.org/10.1371/journal.pone.0310967.g002

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Fig 3. Area graph of breastfeeding status with and without exclusive breastfeeding during the first 7 d after birth.

https://doi.org/10.1371/journal.pone.0310967.g003

Results

Overall, 1,433 postpartum women were included in the analysis. Table 1 shows the basic information of the participating women in the two groups: 426 women (29.7%) exclusively breastfed during the first day after birth, and 143 participants (10.0%) exclusively breastfed during the first 7 d after birth. The prevalence of the first-day EBF and the 7-d EBF groups differed significantly based on parity, breastfeeding intention during pregnancy, and mode of delivery. Notably, multiparous women, those who intended to provide only breast milk, and women who delivered vaginally were more likely to have breastfed exclusively during the first day and 7 d after birth. The prevalence of the 7-d EBF group was significantly different according to household income level, unlike that of the first-day EBF group.

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Table 1. Basic information of the study participants (N = 1,433).

https://doi.org/10.1371/journal.pone.0310967.t001

Table 2 shows the associations of first-day EBF and 7-d EBF with 24-h recall EBF of < 6 months. First-day EBF (prevalence ratio [PR] 1.34; 95% confidence interval [CI], 1.14–1.58) and 7-d EBF groups (PR1.63; 95%CI, 1.35–1.96) showed significantly higher PRs of 24-h recall EBF of < 6 months, compared with non-EBF groups. Especially, the PR of the 7-d EBF group was higher than that of the first-day EBF group. Among the adjustment variables, multipara and intention to give only breast milk were also statistically significantly associated with 24-h recall EBF of < 6 months in both groups.

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Table 2. Association of breastfeeding during the first day and the first 7 d after birth with 24-h recall EBF before the survey.

https://doi.org/10.1371/journal.pone.0310967.t002

The area graphs depict the monthly proportions of each feeding pattern and show the difference in the area size between the EBF and non-EBF groups for the first day (Fig 2) and 7 d (Fig 3), respectively. Overall, the two figures highlight that the proportion of 24-h recall EBF increased from 1 to 4 months for the first-day EBF and 7-d EBF groups (left side of the Figs), which made the green area larger than their counterparts (right side of the Figs). The contrast between the EBF and non-EBF groups was more pronounced in Fig 3 than in Fig 2.

As shown in Fig 2, among infants exclusively breastfed during the first day, 24-h recall EBF rates began at 31% at 1 month of age and gradually increased to a peak of 58% at 4 months. Conversely, infants who were not exclusively breastfed on the first day showed consistently low 24-h recall EBF rates throughout the study period. Also, Fig 3 shows that the 24-h recall EBF rate for infants exclusively breastfed during the first 7 d was 50% at 1 month of age and increased steadily to 72% at 5 months. In contrast, for those who were not exclusively breastfed during the first 7 d, the 24-h recall EBF rate started at 15% at 1 month, slowly increased to 35% at 3 months, and then plateaued.

Discussion

This cross-sectional study of 1,433 women within 6 months postpartum found that EBF rates on the first day and the first 7 d after birth were 29.7% and 10.0%, respectively. Moreover, the 7-d EBF was more strongly associated with the 24-h recall EBF of < 6 months than the first-day EBF. These findings were clearly visualised using area graphs. The area graph shows that the proportion of EBF was low in the first month of life and gradually increased over time. To our knowledge, this is the first study to show, using area graphs, an association between EBF during hospitalisation and subsequent practice until 6 months postpartum, considering the change in breastfeeding status over time [37].

Interestingly, the 7-d EBF, a proxy for the hospitalisation period in Japan [18, 19], was strongly associated with subsequent EBF practice. However, the percentage of the 7-d EBF was only 10%. Even among women who intended to breastfeed exclusively during pregnancy, the rate was only 13%. A previous study of 61 BFHs in Japan reported that approximately 72% of infants were exclusively or predominantly breastfed during hospitalisation [18], which is much higher than our results. However, we did not assess whether milk formula was used for medical indications. Consequently, assuming that BFHs in the above study only used formula milk when there was a medical indication, approximately 28% of infants require formula milk for a medical indication. This implies that most infants in this study were supplemented with formula milk despite having no medical indications.

There may be several reasons for unnecessary milk supplementation. First, the lack of explicit guidance on breastfeeding support in Japan, despite the existence of the Breastfeeding and Weaning Support Guide [14], may lead to different standards for supplementation in health facilities. This may allow routine supplementation and easy selection of formula milk without requiring medical assessment. Therefore, EBF during hospitalisation can be increased if healthcare professionals strengthen breastfeeding support for women who do not meet medical indications, considering their physical condition and intention to feed after childbirth. Second, there is a possible gap in the breastfeeding support provided by healthcare professionals, especially in mixed maternity wards where maternity patients and others stay together. Owing to the decrease in birth rates, the number of mixed maternity wards has increased in Japan, reaching 80.6% in 2013 [38]. A study in Japan involving 52 facilities in 2019 revealed that midwives and nurses offered breastfeeding support in 46 facilities (88.5%); however, 40% of these facilities lacked breastfeeding education, especially for nurses in mixed maternity wards [39], suggesting a potential gap in breastfeeding support. Therefore, the gap in breastfeeding support within health facilities can be mitigated by strengthening the knowledge and skills of healthcare professionals, especially nurses.

The area graphs show that EBF during hospitalisation influenced its continuation in subsequent periods. Interestingly, a unique feeding pattern was observed on the area graphs. The proportion of EBF was the lowest in the first month of age and gradually increased each month until the weaning period. This pattern contradicted those reported in other countries, predominantly LMICs, which illustrated the highest rate of EBF in the first months that decreased from month to month [37, 40, 41]. This unique situation in Japan implies that some mothers experience a transition from non-EBF to EBF status after discharge. This transition may be facilitated by women’s efforts stemming from their intention to breastfeed exclusively, as highlighted in the results section, where this intention during pregnancy was significantly associated with 24-h recall EBF under 6 months of age. Moreover, women’s daily efforts, increased breastfeeding experiences, and infant growth may also facilitate this transition. Additionally, breastfeeding support and continuation of care by healthcare professionals or peer supporters, even after discharge, are crucial to facilitate EBF for < 6 months [42]. In Japan, most postpartum women and newborns have routine check-ups at 2 weeks and 1 month after delivery at the health facilities where the women delivered their babies [43]. If they do not have any problems, there is no further check-up until a home visit within 4 months [44] and a health check-up at 3–6 months organised by the municipalities [45, 46]. In addition to routine check-ups, various optional breastfeeding support mechanisms are available in Japan. For instance, since 2021, municipalities have been obligated to make efforts to provide “Care services after childbirth”, including overnight stays, day services, and outreach programs [47, 48]. Breastfeeding counselling is offered at hospitals, maternity homes, and even during home visits. Although their availability varies depending on the area and offered services, and user fees are not standardised [48, 49], these optional breastfeeding support mechanisms may contribute to increasing the EBF rate under 6 months of age. However, this study did not thoroughly investigate the reasons for the transition to exclusive breastfeeding after discharge among those who were not exclusively breastfeeding during hospitalisation. Therefore, further research is warranted.

Additionally, the absence of legal measures for formula milk marketing in Japan may easily allow formula milk marketing even at health facilities [50–53], such as the free offering of formula milk samples to women at discharge. This may influence the ease of choosing formula milk when postpartum women perceive insufficient milk production. Consequently, formula milk supplementation due to perceived insufficient milk production may reduce the breastfeeding frequency of the mother, breast milk production and cessation of breastfeeding, even if they wish to breastfeed exclusively [54, 55]. Therefore, strengthening the continuum of breastfeeding support, such as providing breastfeeding guidance and information on accessible services for mothers both in antenatal and postpartum periods, would mitigate breastfeeding difficulties, promote and sustain breastfeeding practices [56].

The postpartum period in this study was amid the COVID-19 pandemic, implying that lack of support due to the COVID-19 pandemic affected the results of this study, as other studies in HICs reported that a reduction of breastfeeding support by healthcare professionals and peers negatively affected breastfeeding practices [57–59]. Our study did not find significant associations between receiving support after discharge and EBF for < 6 months. This may have been affected by other factors that were not assessed in this study. For example, the avoidance of home visits by certain postpartum women was caused by fear of infection, as reported by the Ministry of Internal Affairs and Communications [60]. Currently, the restrictions imposed by the COVID-19 pandemic have been relaxed, and life is returning to the pre-pandemic situation. Therefore, further research is required to assess breastfeeding status in the post-pandemic period and its influencing factors.

Conclusions

EBF during hospitalisation is strongly associated with continued EBF practice for < 6 months. However, approximately 90% of infants were supplemented with formula milk rather than with breast milk at health facilities during this period. Therefore, improving breastfeeding support in health facilities by mitigating the gap in knowledge and skills among healthcare professionals and offering continued breastfeeding support during and after hospitalisation may contribute to increasing EBF for < 6 months and more mothers and infants will benefit from breastfeeding.

Acknowledgments

We express our sincere appreciation to the women who participated in this study.