Introduction Insufficient and disrupted sleep in pregnancy is significantly associated with antenatal and postnatal depression, which affects up to 20% of perinatal women. Sleep timing is another important sleep variable that represents sleep preferences besides sleep duration, and mid-point of sleep strongly correlates with chronotype and dim light melatonin onset. In the general population delayed sleep mid-point contributes to poor cardiometabolic and psychological function. Emerging data in pregnancy suggest that later sleep mid-point is related to gestational diabetes, gestational hypertension and pre-eclampsia. However, it is currently unknown whether sleep timing plays a role in depressive symptoms in pregnancy.

Methods Pregnant women at least 28 weeks’ gestation were recruited from a large academic medical centre and invited to complete surveys about their sleep, including typical bedtimes and wake-times, as well as demographic information. Presence of depressive symptoms was determined by a current diagnosis of depression or a score ≥10 on the Edinburgh Postnatal Depression Scale (EPDS). Sleep mid-point was calculated as halfway between sleep onset and rise time.

Results Overall, 1599 women were included, of which 30% had depressive symptoms. Demographics are shown in table 1. Women with depressive symptoms had similar bedtimes to controls (11:00pm vs. 10:54pm, p<0.17) but longer time in bed (8.9hr vs. 8.6hr, p=0.04). Mid-point was significantly later in women with depressive symptoms compared to controls (03:28hr vs. 03:14hr, p=0.005). In a regression adjusting for sleep duration and BMI, mid-point was significantly associated with depressive symptoms with an adjusted odds of 1.12 (95%CI 1.1-1.2).

Discussion This study provides initial evidence of a link between self-reported late sleep midpoint and depressive symptoms in pregnancy. These findings suggest that sleep timing is important for maternal health and further studies investigating the potential role of chronotype and circadian timing in perinatal depression should be explored.