Introduction Parental exposure to tobacco smoke has been associated with an increased risk of stillbirth, while only a few studies took the overall parental tobacco exposure status into consideration. We aim to explore the relationship of parental smoking and passive smoking before and during pregnancy with stillbirth in a large Chinese rural cohort.

Design 248 501 couples were enrolled in a national prospective cohort study conducted in rural China. Parental exposure to tobacco smoke before and during pregnancy, along with other risk factors, was ascertained by questionnaires. Pregnancy outcomes were recorded by physicians.

Results The ORs (Odds Ratios) of maternal active smoking, maternal passive smoking, paternal active smoking and paternal passive smoking were 2.07 (95% CI 1.25 to 3.41), 1.22 (95% CI 1.01 to 1.47), 1.36 (95% CI 1.13 to 1.63) and 1.10 (95% CI 0.87 to 1.39), respectively. The rates of stillbirth increased from 0.31% for the maternal non-smoking group to 0.43% for the smoking cessation during pregnancy group, to 0.64% for the decreased smoking group and 1.28% for the continuing smoking group. A similar pattern was found in the change in paternal smoking status and stillbirth. Stratified by maternal passive smoking, the OR of paternal smoking was 1.35 (95% CI 1.13 to 1.61) in the maternal non-smoking group and 1.67 (95% CI 1.09 to 2.56) in the maternal passive smoking group.

Conclusions Parental exposure to tobacco smoke increased the risk of stillbirth, especially for those continuing smoking during pregnancy. Paternal smoking is an independent risk factor for stillbirth despite maternal passive smoking status.