Cigarette smoking associated with delayed conception.

We conducted an epidemiologic study to test the hypothesis that women who smoke have reduced fertility. Data on smoking history and number of noncontracepting cycles until conception were collected from 678 pregnant women. Thirty-eight percent of nonsmokers conceived in their first cycle compared with 28% of smokers. Smokers were 3.4 times more likely to have taken greater than a year to conceive compared with nonsmokers. After adjusting for potential confounding variables by Cox proportional hazards regression, fertility of smokers was estimated to be 72% of the fertility of nonsmokers. Heavy smokers experienced lower fertility than did light smokers (57% and 75% of the pregnancy rate of nonsmokers, respectively). Fertility was not affected by the husband's smoking. These data provide evidence that reduced fertility should be added to the growing list of reproductive hazards of cigarette smoking.