Birthweight below the tenth percentile: the relative and attributable risks of maternal tobacco consumption and other factors.

Analysis of 7776 singleton births defined a cohort of babies with birthweight below the 10th percentile after adjusting for gestational age and sex. The relative risk of a baby being small for gestational age in respect to a number of factors, such as parental anthropometry, demographic factors, behavior patterns (tobacco, cannabis, alcohol, and caffeine consumption), maternal pathology, and fetal abnormality, was calculated. The highest relative risks are associated with severe antepartum hemorrhage, severe pre-eclampsia, and severe fetal abnormality. As these are relatively rare events, a more accurate calculation of overall risk to the population as opposed to the individual can be obtained by studying the percent attributable risk of each of the factors. This demonstrates that maternal tobacco consumption is the major environmental risk factor in our population.