Adult and prenatal exposures to tobacco smoke as risk indicators of fertility among 430 Danish couples.

During 1992-1995, 430 Danish couples were recruited after a nationwide mailing of a letter to 52,255 trade union members who were 20-35 years old, lived with a partner, and had no children. The couples were enrolled into the study when they discontinued birth control, and they were followed for six menstrual cycles or until a clinically recognized pregnancy. At enrollment and each month throughout the follow-up, both partners completed a questionnaire that asked them about their smoking, alcohol consumption, and intake of caffeinated beverages. The effect of current smoking and smoking exposure in utero was evaluated by using a logistic regression model with pregnancy outcome of each cycle in a Cox discrete model calculating the fecundability odds ratio. After adjustment for female body mass index and alcohol intake, diseases in female reproductive organs, semen quality, and duration of menstrual cycle, the fecundability odds ratio for smoking women exposed in utero was 0.53 (95% confidence interval (CI) 0.31-0.91) compared with unexposed nonsmokers. Fecundability odds ratio for nonsmoking women exposed in utero was 0.70 (95% CI 0.48-1.03) and that for female smokers not exposed in utero was 0.67 (95% CI 0.42-1.06). Exposure in utero was also associated with a decreased fecundability odds ratio in males (0.68, 95% CI 0.48-0.97), whereas present smoking did not reduce fecundability significantly. It seems advisable to encourage smoking cessation prior to the attempt to conceive as well as during pregnancy.