Objectives To investigate the effect of secondhand smoke exposure from a partner on the risk of having a newborn baby with neural tube defects (NTDs) in Chinese non-smoking women.

Methods Data were derived from an on-going population-based case–control study of external malformations in northern China. The case group included 580 infants or fetuses with NTDs identified between November 2002 and December 2007. Controls were 795 newborn infants without major external malformations. Data were collected by trained health workers through face-to-face interviews within 1 week after delivery.

Results A total of 81.4% of partners of case women and 71.8% of partners of control women smoked during the women's peri-conceptional period. The adjusted OR for NTDs associated with partner smoking was 1.6 (95% CI 1.2 to 2.1). Compared with non-smoking women with non-smoking partners, fetal NTD risk among women with smoking partners was 1.7 (1.3 to 2.4) and 1.1 (0.7 to 1.7) for women exposed and not exposed to partner smoking, respectively. Among women who were exposed to partner smoking, the risk of NTDs was 1.4 (0.9 to 2.0), 1.8 (1.2 to 2.6), 1.9 (1.2 to 3.0) and 2.7 (1.6 to 4.7) for partner smoking of <1, 1–9, 10–19 and ≥20/day, respectively (p for trend <0.001).

Conclusion Peri-conceptional exposure to partner smoking may increase the risk of NTDs in the offspring of Chinese non-smoking women.