[Correlation between maternal age, social class and smoking, and birth weight]

An epidemiological survey was carried out in Ribeirão Preto, Brazil, from June 1978 to May 1979. Interviews were held with mother of singleton live borne children, delivered in hospitals, which accounted for 98% of all births in the area. The higher percentages of low birthweight children related to the offspring of smokers, young mother and women belonging to the working class. The majority of young women were found in the working class and the prevalence of smoking was higher in the group of women below 20 years of age. There was no statistical difference in the smoking habit as between different social classes. A larger number of low birthweight children were observed in nonsmoking women of the working class than among women smokers of the middle class. A log model was adjusted to the data in order to study the possible multiple association of smoking, maternal age and social class with birthweight. The results indicated that maternal smoking, maternal age and social class had independent effects on birthweight. The was no interaction between them. These findings suggest that the higher prevalence of low birthweight in nonsmoking mothers of the working class in relation to smoking mothers of the middle class probably reflects clustering of other risk factors-such as poor education inadequate prenatal care, high parity and differences in reproductive behavior in women of the working class.