Objective: To determine the effects of passive maternal smoking on birthweight.
Design: Cohort of consecutive singleton live births.
Setting: Teaching hospital in South India.
Subjects: 994 infants and their mothers.
Main outcome measure: Birthweight.
Results: All the women were themselves non-smokers; 520 (52%) were passive smokers while the remainder were not exposed to tobacco smoke. Infants born to passive smokers were on the average 55 g lighter than those born to non-smokers. Passive smoking was associated with a decrease in birthweight of 63 g (95% CI 12-114 g) even after adjusting for other variables known to affect birthweight.
PIP: Physicians compared the birth weight of 520 singleton newborns whose mothers were passive smokers with that of 474 singleton newborns whose mothers were nonsmokers to examine the effects of passive smoking on birth weight. All the women delivered at the Christian Medical College Hospital in Vellore, India between January-May 1990. None of the mothers actually smoked themselves. Passive smokers were more likely to have more than 3 children (p=.007) and be from the lower social classes than nonsmokers (p.0001). In addition, nonsmokers tended to be vegetarians (p.0001). Infants born to passive smokers weighed a mean of 55 g lighter than those born to nonpassive smokers (2890 kg vs. 2945 kg). Further, passive smoking was significantly related to a fall of 63 g in birth weight after adjusting for maternal age, height, diet, parity, social class, gestation at birth and its square, sex of the infant (p=.015). In fact, passive smoking explained 15.5% of the variation in birth weight. Researchers were not able to estimate a dose response relationship since the mothers could not quantify their exposure to tobacco smoke. This study was the 1st ever reported on the effects of passive maternal smoking on birth wright from a population in which women rarely smoke. Based on these results, the researchers recommend that until the scientific community can prove that passive smoking does not harm fetuses, parents should avoid exposure to tobacco smoke during pregnancy.