Background: Data from several studies indicate that children of mothers who smoked during pregnancy may be at a risk of overweight compared with children of non-smoking mothers. The size of this relation, however, is unclear, as is the age at which it becomes detectable.
Methods: Prospective data for 34 866 children enrolled in the US Collaborative Perinatal Project were analysed to examine maternal pregnancy smoking in relation to weight, height, and body mass index (BMI) in offspring at ages 1, 3, 4, 7, and 8 years.
Results: Compared with offspring of non-smokers, children of smokers had (i) weight that was lower at birth but then quickly equalled or exceeded that of non-smokers, (ii) consistently decreased height, and (iii) increased risk of overweight, particularly in girls. For example, at age 7 years, the adjusted odds ratio of BMI>or=85th percentile in boys of mothers who smoked on an average>or=20 cigarettes per day while pregnant was 1.22 (95% confidence interval 1.03-1.46), and in girls it was 1.30 (1.08-1.56).
Conclusions: In these data, maternal smoking during pregnancy was associated with a modest increase in risk of overweight in children before the age of 8 years.