SMOKING REDUCES FECUNDITY - A EUROPEAN MULTICENTER STUDY ON INFERTILITY AND SUBFECUNDITY

Several studies published within the past 10 years indicate that smoki ng reduces fecundity, but not all studies have found this effect, and smoking cessation is not used routinely in infertility treatment in Eu rope, The present study was designed to examine male and female smokin g at the start of a couple's waiting time to a planned pregnancy. Two types of samples were used: population-based samples of women aged 25- 44 years who were randomly selected in different countries from census registers and electoral rolls, in which the unit of analysis was the couple; and pregnancy-based samples of pregnant women (at least 20 wee ks' pregnant) who were consecutively recruited during prenatal care vi sits, in which the unit of analysis was a pregnancy. More than 4,000 c ouples were included in each sample, and 10 different regions in Europ e took part in data collection. The data were collected between August 1991 and February 1993 by personal interview in all population-based samples and in all but three regions of the pregnancy sample, where se lf-administered questionnaires were used. The results based on the pop ulation sample showed a remarkably coherent association between female smoking and subfecundity in each individual country and in all countr ies together, both with the first pregnancy (odds ratio (OR) = 1.7, 95 % confidence interval (CI) 1.3-2.1, at the upper level of exposure) an d during the most recent waiting time to pregnancy (OR = 1.6, 95% CI 1 .3-2.1). Results based on the pregnancy sample were similar (OR = 1.7, 95% CI 1.3-2.3). No significant association was found with male smoki ng (in the population sample, OR = 0.9, 95% CI 0.7-1.1 (first pregnanc y) and OR = 1.0, 95% CI 0.9-1.3 (most recent waiting time); in the pre gnancy sample, OR = 0.9, 95% CI 0.7-1.1). The fecundity distribution a mong smokers appeared to be shifted toward longer waiting times withou t a change in the shape of the distribution. Women who have difficulty conceiving should try to stop smoking or to reduce their smoking to l ess than 10 cigarettes per day.