Does cigarette smoking impair natural or assisted fecundity?**Supported by the Health Protection Branch of Health and Welfare Canada, Ottawa, Ontario, Canada

OBJECTIVES: To assess the effects of female and male smoking on natural and assisted fecundity. DESIGN: A systematic review of published studies was conducted, identifying reports using on-line and hand search techniques. INCLUDED STUDIES: Potentially relevant articles were screened for inclusion based on the following criteria: comparative study (cohort or case control) with clinical pregnancy or live birth reported among smokers and nonsmokers. EXPOSURE: Cigarette smoking. MAIN OUTCOME MEASURES: Time to conceive; conceptions per subject or per cycle; spontaneous abortion rate. RESULTS: Thirteen relevant studies of natural conception were identified. All but one demonstrated a negative association between smoking and fecundity (odds ratio [OR] for conception or live birth 0.33 to 1.0). Seven studies of IVF-GIFT yielded a common odds ratio for conception of 0.57 (95% confidence interval 0.42 to 0.78). Seven studies evaluating spontaneous abortion suggested a small increased risk among female smokers (OR 0.83 to 1.8). Twenty-one studies assessing smoking in men demonstrated no consistent effect on sperm quality. None of the four studies evaluating fertility in male smokers demonstrated significant impairment. CONCLUSION: This body of literature suggests a small but clinically significant detrimental effect of female smoking on both time to conception and spontaneous abortion risk. Variability between studies, particularly in terms of adjustment for confounding factors, undermines the strength of these conclusions. However, the consistent dose-response effect in both the spontaneous conception and abortion literature and a return to normal fecundity among exsmokers suggest a causal association. The effect of male smoking on fecundity is probably far less significant.