Husband smoking, smoking cessation, and fecundability among couples with non-smoking wives.

Among couples with non-smoking wives, the relationship between husband smoking and fecundability remains uncertain. Evidence is limited regarding whether smoking cessation before conception is associated with improved fecundability. We included a total of 4,569,530 reproductive-aged couples with non-smoking wives from the National Free Pre-conception Check-up Project in China from 2015 to 2017. Cox proportional hazards models were used to estimate fecundability hazard ratios (HRs) and 95% confidence intervals (CIs). Among 4,569,530 eligible couples, 1,228,222 (26.88%) husbands reported smoking at baseline. Within 1 year, 3,046,804 couples (66.68%) conceived, with a median TTP of 2.76 cycles. Husband smoking was associated with lower fecundability (HR=0.97, 95% CI, 0.97-0.97), demonstrating a dose-response relationship. Among 781,481 couples in which the husband smoked and conception occurred within 1 year, 507,530 (64.94%) reported smoking cessation. Smoking cessation was associated with higher fecundability (HR=1.23, 95% CI, 1.23-1.24), with consistent benefits across prior smoking levels, although the magnitude of improvement was smaller among husbands who smoked more heavily. Associations varied by age and were more pronounced in older couples. These findings support the inclusion of husband smoking cessation in preconception care and highlight its potential role in promoting smoke-free households and broader tobacco control efforts.