Passive smoking and low birthweight [letter]

Studies have demonstrated a significant relationship between passive smoking and low birthweight. Here the authors present evidence from Shanghai where few young mothers smoked. All 1163 babies born between June 1 and Dec 31 1981 and living in the neighborhoods of Nan-Jing Western Road and Yan-An Western Road in Jing-An District Shanghai were selected for study. A self-administered questionnaire was posted to every childs home to be completed by the parents or guardians. No mothers were smokers. Of 1058 infants 764 (72.2%) were born into households with 1 smoker or more; in 612 (57.8%) cases the father smoked. Passive exposure of the mother to tobacco smoke was estimated by the daily cigarette consumption of the father and by total family members respectively. The table shows that passive smoke was not significantly related to either mean birthweight or the rate of low birthweight. Possible confounders including infants sex parity fathers education maternal age at birth and average income were examined with multiple linear and logistic regressions: no factors were found to change the results. Our study does rule out the maternal antenatal smoking effect. But the causes of fetal growth retardation are complicated and many physiological and environmental factors related to low birthweight may also be associated with passive exposure to tobacco smoke. To clarify the issue these factors need to be taken into consideration in designing further studies. (authors modified)