The Current Status of Postpartum Menstrual Resumption Delay and Associated Risk Factors in Japanese Women: An Adjunct Study of the Japan Environment and Children's Study.

Background: Prolonged postpartum amenorrhea is a sign of secondary infertility. However, there are no reports on postpartum menstrual resumption delay in Japanese women. We conducted an Adjunct Study of the Japan Environment and Children's Study (JECS) to elucidate the actual state of postpartum menstrual resumption delay in Japan and related factors.

Methods: An Adjunct Study questionnaire was sent to 2,729 mothers who participated in the study of Shinshu Subunit Center in the JECS, and 762 mothers were included in the analysis. The participants were categorized into the normal and delayed groups based on the weeks of postpartum menstrual resumption. To investigate the factors associated with postpartum menstrual resumption delay, a multiple logistic regression analysis was conducted with the weeks of postpartum menstrual resumption as the dependent variable.

Results: The study included 762 women, of which 61 (8.0%) had delayed menstruation, not occurring until 72 weeks postpartum. The multivariate analysis revealed a significant correlation between postpartum menstrual resumption delay and age at delivery, past history of irregular menstruation, history of taking oral contraceptives, breastfeeding at 18 months, and the level of satisfaction with the husband's participation in childcare.

Conclusion: Postpartum menstruation in Japanese women occurred later than before. In addition to previous findings, another factor was the husband's satisfaction with his participation in childcare. We should not only focus on the physical aspects of mothers, but also provide midwifery care that proposes and supports family planning suitable for each family.