RESUMEN
BACKGROUND: Different studies have shown the advantages of abstinence from cigarette smoking during pregnancy to promote full fetal development. Given that pregnant women do not always abstain from smoking, this study aimed to analyze the effect of different intensities of smoking on birth weight of the newborn. METHODS: A cross-sectional study was adopted to explore smoking in a population of pregnant women from a medium-sized city in São Paulo state, Brazil, who gave birth between January and June of 2012. Data were collected from maternal and pediatric medical files and, where data were absent, they were collected by interview during hospitalization for delivery. For data analysis, the effect of potential confounding variables on newborn birth weight was estimated using a gamma response model. The effect of the identified confounding variables was also estimated by means of a gamma response regression model. RESULTS: The prevalence of smoking during pregnancy was 13.4% in the study population. In full-term infants, birth weight decreased as the category of cigarette number per day increased, with a significant weight reduction as of the category 6 to 10 cigarettes per day. Compared with infants born to non smoking mothers, mean birth weight was 320 g lower in infants whose mothers smoked 6 to 10 cigarettes per day and 435 g lower in infants whose mothers smoked 11 to 40 cigarettes per day during pregnancy. CONCLUSIONS: Based on the study results and the principle of harm reduction, if a pregnant woman is unable to quit smoking, she should be encouraged to reduce consumption to less than six cigarettes per day.