A prospective study of the relation between smoking and fertility.

A prospective study of fertility was conducted from 1977 to 1982. Analysis of the relation between cigarette smoking and occurrence of a pregnancy was performed on 1887 couples. The actuarial pregnancy rate was 82.9% at the end of a year. Cigarette smoking by both members of the couple was found to be related to decreased fertility when this factor was considered alone. But after including all the confounding covariates in a Cox semi-proportional hazards model for survival data, no relationship remained between cigarette smoking and fertility. Odds ratios were respectively 0.86 (95% confidence interval: 0.63, 1.19) and 0.99 (0.85, 1.14) for women smoking and men smoking. This could suggest that the relationship found by other authors might be at least partly explained by a relation between cigarette smoking and other factors related to fertility.