Effect of nausea and vomiting during pregnancy on mother-to-infant bonding and the mediation effect of postpartum depression: the Japan Environment and Children’s Study

Background: Mother-to-infant bonding (MIB) is critical for the health and well-being of the mother and child. Furthermore, MIB has been shown to boost the social-emotional development of infants, while also giving mothers a sense of happiness in raising their children. Nausea and vomiting during pregnancy (NVP) is a normal complication of pregnancy, occurring in approximately 50–90% of pregnant women in the early stages of pregnancy. Despite widespread knowledge of MIB and postpartum depression, little research attention has been given to the effects of NVP on MIB. This study aimed to investigate the relationship between NVP and MIB and the mediating effects of postpartum depression. Methods: We analyzed the data of 88,424 infants and 87,658 mothers from the Japan Environment and Children’s Study (JECS), which is a government-funded nationwide birth prospective cohort study. The Japanese version of the Mother-to-Infant Bonding Scale (MIBS-J) was used to assess MIB, and the Edinburgh Postpartum Depression Scale (EPDS) was utilized to assess postpartum depression. We divided participants into four groups according to a self-reported questionnaire assessing NVP (No NVP, Mild NVP, Moderate NVP, and Severe NVP). MIB disorder was defined as a MIBS-J score ≥ 5. Logistic analysis was performed to evaluate the effect of NVP on MIB disorder at one year after delivery. A mediation analysis was conducted to examine whether postpartum depression mediated the association between NVP and MIBS-J scores. Results: The logistic regression analysis results revealed reduced risks of MIB disorder among mothers with Moderate NVP (adjusted OR 0.93; 95% confidence interval, 0.86–0.99) and Severe NVP (adjusted OR 0.81; 95% confidence interval, 0.74–0.89), compared to those with No NVP. The mediation analysis revealed that NVP positively correlated with MIBS-J score in the indirect effect via postpartum depression, while NVP (Mild NVP, Moderate NVP, and Severe NVP) negatively correlated with MIBS-J score in the direct effect. Conclusion: The risks of MIB disorder were reduced in the Moderate NVP and Severe NVP mothers, although NVP inhibited the development of MIB via postpartum depression. The development of effective interventions for postpartum depression is important to improve MIB among mothers with NVP.