Second-trimester serum cotinine levels in nonsmokers in relation to birth weight.

In this study the relationship between birth weight and passive exposure to tobacco smoke is assessed for the first time by serum cotinine measurements. Among 1231 nonsmoking white women whose blood was sampled during the second trimester of pregnancy, 31.4% had serum cotinine levels between 1.0 and 9.9 ng/ml and were therefore considered to be passively exposed to tobacco smoke. The crude mean birth weight of infants of the women passively exposed to smoke was 107 gm lower than that of infants of unexposed women, and that difference remained after the application of a multivariate analysis that included the major known birth weight-associated covariates. These findings are consistent with a causal relationship between passive exposure to tobacco smoke and birth weight and suggest that the dose-response relationship may not be linear.