Passive smoking during pregnancy and the risk of delivering a small-for-gestational-age infant.

The objective of this population-based study was to assess the association between environmental exposure to tobacco smoke during pregnancy and the risk of delivering a small-for-gestational-age (SGA) infant (< 10th percentile). A total of 4,644 nonsmoking women who lived in the Quebec City area and who gave birth between January and October 1989 to a singleton liveborn neonate were included in the analysis. Information on gestational age at delivery, maternal passive smoking at home and at work, and several potential confounders was obtained by a telephone interview with the mother a few weeks after delivery. Birth weight was abstracted from the birth certificate. Overall, passive smokers were at little or no higher risk of having a SGA infant than unexposed women (adjusted odds ratio = 1.09, 95% confidence interval (CI) 0.85-1.39). Passive exposure to tobacco smoke at home only was not related to SGA. However, small increments in risks were observed in women exposed to passive smoking at work only, and risks increased consistently with weekly duration, number of weeks, and intensity of exposure. When compared with unexposed mothers, women exposed to tobacco smoke in the workplace for 1-14, 15-34, and > or = 35 hours per week had adjusted odds ratios of 1.13 (95% CI 0.79-1.61), 1.17 (95% CI 0.73-1.87), and 1.36 (95% CI 0.91-2.09), respectively. This latter odds ratio was close to that observed among women who smoked actively 1-5 cigarettes per day. Although not conclusive, the results are compatible with the hypothesis that environmental exposure to tobacco smoke during pregnancy may be related to a modest increase in the risk of delivering a SGA infant.