Objective: To examine the relationship between different levels of maternal passive tobacco smoke exposure and low-birth-weight infants.
Design: Data from the National Health Interview Survey were analyzed.
Participants: Women who did not smoke during pregnancy and gave birth to children within 6 years of the date of the interview in 1988 were the source of the data (N = 3253). Passive smoke exposure was categorized as very low, low, moderate, and high.
Main outcome measures: Low-birth-weight (< 2500 g) infants and mean birth weight in grams.
Results: There was no significant difference in the rates of low birth weights when passive smoke exposure was dichotomized as no exposure vs some exposure (5.0% vs 5.6%, respectively; P = .55). However, when the level of exposure to passive smoke was considered as a continuum, high exposure was associated with both lower mean birth weights in grams (P = .007) and a greater likelihood of a low birth weight (P = .01), indicating a threshold effect of exposure. Logistic regression analysis indicated that, after controlling for potentially confounding variables, individuals with high exposure are 1.57 times (95% confidence interval [CI], 0.98 to 2.51) as likely as those with low exposure to have a low-birth-weight infant. Among nonwhites, individuals with high exposure to passive smoke were 2.31 times (95% CI, 1.06 to 4.99) as likely to have a low-birth-weight infant as those with low exposure to passive smoke.
Conclusion: A threshold effect of exposure to passive smoke and low birth weight was discovered.