Objectives: To determine whether snoring, sleep position, and other sleep practices in pregnant women are associated with risk of late stillbirth.
Design: Prospective population based case-control study.
Setting: Auckland, New Zealand
Cases: 155 women with a singleton late stillbirth (≥ 28 weeks' gestation) without congenital abnormality born between July 2006 and June 2009 and booked to deliver in Auckland.
Controls: 310 women with single ongoing pregnancies and gestation matched to that at which the stillbirth occurred. Multivariable logistic regression adjusted for known confounding factors.
Main outcome measure: Maternal snoring, daytime sleepiness (measured with the Epworth sleepiness scale), and sleep position at the time of going to sleep and on waking (left side, right side, back, and other).
Results: The prevalence of late stillbirth in this study was 3.09/1000 births. No relation was found between snoring or daytime sleepiness and risk of late stillbirth. However, women who slept on their back or on their right side on the previous night (before stillbirth or interview) were more likely to experience a late stillbirth compared with women who slept on their left side (adjusted odds ratio for back sleeping 2.54 (95% CI 1.04 to 6.18), and for right side sleeping 1.74 (0.98 to 3.01)). The absolute risk of late stillbirth for women who went to sleep on their left was 1.96/1000 and was 3.93/1000 for women who did not go to sleep on their left. Women who got up to go to the toilet once or less on the last night were more likely to experience a late stillbirth compared with women who got up more frequently (adjusted odds ratio 2.28 (1.40 to 3.71)). Women who regularly slept during the day in the previous month were also more likely to experience a late stillbirth than those who did not (2.04 (1.26 to 3.27)).
Conclusions: This is the first study to report maternal sleep related practices as risk factors for stillbirth, and these findings require urgent confirmation in further studies.