As modifiable predictors of exclusive breastfeeding at 3 months postpartum, a lower cortisol level after breastfeeding and a higher BSES-SF score at 1 month postpartum were identified on multiple logistic regression analysis. In addition, multiparity, higher education levels, and no plan to return to work by 6 months postpartum were significantly associated with exclusive breastfeeding at 3 months postpartum.
Lower cortisol levels after breastfeeding at 1 month postpartum were associated with exclusive breastfeeding at 3 months postpartum. Notably, the relationship was observed despite no cross-sectional relationship between cortisol levels and exclusive breastfeeding at 1 month postpartum. Cortisol levels usually decrease after breastfeeding since oxytocin inhibits cortisol secretion in women without mood distress . Nevertheless, more than 40% of our participants had increased cortisol levels after versus before breastfeeding. High cortisol levels after breastfeeding despite oxytocin action seem to reflect physiological and psychological stress related to breastfeeding. A stress response after breastfeeding is a modifiable factor. Approaches to stress reduction including preventing breast complications and relieving anxiety by providing advice about breastfeeding concerns could be effective. Maternal cortisol responses to breastfeeding may also vary according to the function of CD38, an ectoenzyme that mediates the release of oxytocin . A recent study has indicated that the CD38 rs3796863 CC genotype is associated with a reduced release of oxytocin during breastfeeding and, accordingly, fewer cortisol-reducing responses to breastfeeding . Thus, women with this genotype may have difficulty establishing and maintaining exclusive breastfeeding due to insufficient milk ejection by decreased oxytocin release. In this manner, the specific gene might influence the relationship between breastfeeding and cortisol responses to breastfeeding through oxytocin secretion. Further studies are needed to clarify the relationship.
A higher BSES-SF score was associated with subsequent exclusive breastfeeding as reported by a previous study of another population . Breastfeeding self-efficacy reflects a mother’s confidence in her ability to breastfeed her infant. The BSES-SF contains the following items “I can always keep wanting to breastfeed” and “I can always be satisfied with my breastfeeding experience” [9, 15]. Women with positive answers against such items seemed to be less stressed about breastfeeding. A systematic review showed that the prenatal and postpartum intervention focusing on improving breastfeeding self-efficacy leads to exclusive breastfeeding . However, in Japan, the effects of prenatal intervention using a breastfeeding self-efficacy workbook are limited and effective in only baby-friendly hospitals and in the early postpartum period . Thus, consideration of more effective approaches is needed for postpartum Japanese women. Women with lower breastfeeding self-efficacy were also reportedly more likely to perceive milk insufficiency [9, 27]. Such a perception has been pointed out as a factor of exclusive breastfeeding cessation . The perception of milk insufficiency itself was not assessed in our study because this concept was supposed to be contained in questions of the BSES-SF. A further detailed study regarding the relationship among breastfeeding self-efficacy, perception of milk insufficiency, and subsequent exclusive breastfeeding might contribute to suggestion of concrete intervention methods for increasing the rate of exclusive breastfeeding.
As with previous studies, parity and education level were associated with exclusive breastfeeding [4, 11]. However, the effect of parity on exclusive breastfeeding practice is not a simple correlation; rather, it varies among study populations [5, 29]. In multiparas, the perception of successful breastfeeding of the previous child is likely to be positively correlated with exclusive breastfeeding duration . By contrast, previous unsuccessful breastfeeding experiences often negatively affect subsequent breastfeeding initiation and duration [30, 31]. In this manner, the association between parity and exclusive breastfeeding practice may be mediated by previous breastfeeding experience. The relationship observed in the present study might imply that most multiparous participants had positive impressions of previous breastfeeding experiences.
Women with a university education or above were more likely to exclusively breastfeed. Women with higher education levels easily access health-related information and have more favorable attitudes toward breastfeeding [32, 33]. Such behavioral characteristics in women with higher education levels might help them achieve exclusive breastfeeding.
Returning to work by 6 months postpartum was associated with less exclusive breastfeeding at 3 months postpartum. Postpartum women who planned to return to work in the earlier postpartum period tend to select partial breastfeeding or formula feeding [25, 34]. In Japan, continuing exclusive breastfeeding for some working women is difficult because of the work environment and nursery policies. A private space and consideration for expressing breast milk during working hours are often lacking, although many companies have been trying to arrange such environments. Nursery policies often refuse breast milk storage due to hygienic reasons. Such situations sometimes make women discontinue exclusive breastfeeding . In addition, partners’ attitudes against breastfeeding and childcare could be important elements that prevent women from discontinuing to breastfeed after returning to work . Environmental and emotional support from family members, employers, and nursery staff members might be essential for working women to continue exclusive breastfeeding.
Exclusive breastfeeding at 1 month postpartum is a strong predictor of the same at 3 months postpartum. However, even if women are not exclusively breastfeeding at 1 month postpartum, they may transition to exclusive breastfeeding as observed in the present study. The first 3 months after childbirth remain a critical period for the establishment of exclusive breastfeeding. Stress levels after breastfeeding and breastfeeding self-efficacy are key modifiable predictors. Thus, healthcare providers’ advice and intervention for reducing stress responses associated with breastfeeding and improving breastfeeding self-efficacy may be effective to establish and continue exclusive breastfeeding.
The present study had two limitations. First, the dropout rate was higher than expected. This might attenuate its statistical power. Second, we could not follow the participants for a full 6 months postpartum, although exclusive breastfeeding for 6 months is recommended. However, the key strength of this study is that we showed the relationship between stress responses associated with breastfeeding and subsequent exclusive breastfeeding, using objective measures of stress.