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.
PIP: The effect of male and female current smoking and smoking exposure in utero on fecundability was investigated in a prospective cohort study conducted in 1992-95 in Aarhus and Copenhagen, Denmark. From a nationwide mailing to 52,255 trade union members who were 20-35 years old, lived with a partner, and had no children, a total of 430 couples were recruited. Couples discontinued contraception at study enrollment and were followed for 6 menstrual cycles or until pregnancy. A logistic regression model was used with pregnancy outcome of each cycle in a Cox discrete model calculating the fecundability odds ratio. 127 women (30%) and 137 men (32%) were smokers at study enrollment; 163 women (42%) and 154 men (40%) reported exposure to cigarette smoke in utero. In the 6 cycles of follow-up, 51.2% of smokers and 63.0% of nonsmokers conceived. After adjustment for female body mass index and alcohol intake, female reproductive organ diseases, semen quality, and duration of the menstrual cycle, the fecundability odds ratio (OR) for smoking women exposed in utero was 0.53 (95% confidence interval (CI), 0.31-0.91) compared with unexposed smokers. The fecundability OR 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). In utero exposure was also associated with a decreased fecundability OR in men (0.68; 95% CI, 0.48-0.97), but current smoking did not reduce fecundability significantly. These findings indicate cigarette smoking is a reproductive health hazard both before and during pregnancy.