Association of pre-pregnancy and pregnancy sleep on the risk of postpartum depression: a nationwide birth cohort-the Japan Environment and Children’s Study

BACKGROUND: The association between pre-pregnancy sleep patterns and postpartum depression as well as the modifying effect of parity, remains insufficiently understood. This study examined the longitudinal associations of sleep before and during pregnancy on the risk of postpartum depression at one month postpartum, with additional analyses stratified by parity. METHODS: Data were obtained from the Japan Environment and Children's Study, a nationwide birth cohort study conducted between 2011 and 2014. A total of 65,477 women who completed questionnaires on demographic characteristics, obstetric factors, sleep patterns before and during pregnancy, and postpartum depression at one month postpartum were included. Relative risks (RRs) and 95% confidence intervals (CIs) for postpartum depression were estimated according to sleep duration, bedtime, sleep depth, and morning mood after adjusting for relevant covariates. RESULTS: A pre-pregnancy sleep duration of 8-9 h was associated with a lower risk of postpartum depression (RR = 0.94, 95% CI: 0.89-0.99). During pregnancy, sleeping less than 6 h and having bedtimes outside the 9:00 pm-midnight or midnight-3:00 am ranges were associated with increased risks of postpartum depression (RR = 1.19, 95% CI: 1.10-1.30; RR = 1.20, 95% CI: 1.07-1.35, respectively). Very light and light sleep were strongly associated with higher risks (RR = 1.88, 95% CI: 1.76-2.01; RR = 1.37, 95% CI: 1.31-1.44, respectively). Additionally, waking in a very bad or bad mood during pregnancy markedly increased the risk of postpartum depression (RR = 2.22, 95% CI: 1.99-2.47; RR = 1.72, 95% CI: 1.64-1.79, respectively). In parity-stratified analyses, multiparous women with bedtimes between midnight and 3:00 am before or during pregnancy had elevated risks of postpartum depression, with significant effect modification (pre-pregnancy: RR = 1.11, 95% CI: 1.03-1.19, p = 0.001; pregnancy: RR = 1.12, 95% CI: 1.04-1.22, p = 0.01). Among multiparous women, waking in a very bad or bad mood during pregnancy was also strongly associated with postpartum depression, with a significant effect modification (RR = 2.65, 95% CI: 2.28-3.09; RR = 1.93, 95% CI: 1.80-2.06, respectively, p < 0.001). CONCLUSIONS: Pre-pregnancy and pregnancy sleep patterns are associated with the risk of postpartum depression. Particularly, among multiparous women, late bedtimes before and during pregnancy may increase this risk. Improving sleep habits before and during pregnancy may contribute to the prevention of postpartum depression. TRIAL REGISTRATION: Clinical trial number: Not applicable.