Exposure to environmental tobacco smoke and birth outcome: increased effects on pregnant women aged 30 years or older.

The purposes of this study were to examine the association between self-reported environmental tobacco smoke (ETS) exposure during pregnancy and birth weight, prematurity, and small-for-gestational age infants and to determine whether these associations differ by maternal age. Data from the Pregnancy Nutrition Surveillance System from two states that collected data on both passive and active smoking for the period 1989-1994 were analyzed. ETS exposure was defined as reported exposure to the cigarette smoke of a household member. Multiple logistic and linear regression analyses were used to evaluate the association between ETS and birth outcomes. The mean adjusted birth weight among infants of nonsmoking mothers age 30 years or older was 90 g less among infants exposed to ETS than among infants not exposed. No significant association was found among infants of younger nonsmoking mothers. Similarly, the risks for low birth weight (adjusted odds ratio (OR) = 2.42, 95% confidence interval 1.51-3.87) and preterm delivery (adjusted OR = 1.88, 95% confidence interval 1.22-2.88) were elevated among older nonsmokers exposed to ETS, but not among younger nonsmokers exposed to ETS (adjusted OR = 0.97, 95% confidence interval 0.76-1.23; adjusted OR = 0.92, 95% confidence interval 0.76-1.13, for low birth weight and preterm delivery, respectively). These findings indicate that the association between ETS exposure and adverse pregnancy outcomes appears to be modified by maternal age.