Paternal smoking and spontaneous abortion: a population-based retrospective cohort study among non-smoking women aged 20-49 years in rural China

Background: To comprehensively evaluate the association of paternal smoking and spontaneous abortion.

Methods: We conducted a population-based retrospective cohort study among 5 770 691 non-smoking rural Chinese women, along with their husbands, participating in the National Free Pre-Pregnancy Checkups Project, regarding outcome events that occurred in 2010-2016. The main outcome was spontaneous abortion (SA). Multivariable logistic regression was used to estimate OR and 95% CI, and restricted cubic spline was used to estimate the non-linear relationship.

Results: The multivariable-adjusted OR of exposure to paternal smoking for SA was 1.17 (95% CI 1.16 to 1.19), compared with women without exposure to paternal smoking; and corresponding OR of exposure to preconception paternal smoking for SA was 1.11 (95% CI 1.08 to 1.14), compared with women without exposure to preconception paternal smoking. The ORs of preconception paternal smoking also increased with increases in paternal smoking (p_nonlinear<0.05, almost linearly shaped) and preconception paternal smoking (p_nonlinear>0.05). In addition, periconception paternal smoking cessation was associated with an 18% (15%-22%) lower risk of SA.

Conclusion: Paternal smoking was associated with SA. The importance of tobacco control, specifically pertaining to paternal smoking, should be emphasised during preconception and pregnancy counselling.