Maternal smoking and fetal growth characteristics in different periods of pregnancy

The authors examined the associations of maternal smoking in pregnancy with various fetal growth characteristics among 7,098 pregnant women participating in the Generation R Study (2002-2006), a population-based prospective cohort study of pregnant women and their children in Rotterdam, the Netherlands. Maternal smoking was assessed by questionnaires administered in early, mid-, and late pregnancy. Fetal growth characteristics evaluated included head circumference, abdominal circumference, and femur length measured repeatedly in mid- and late pregnancy. Maternal smoking during pregnancy was associated with reduced growth in head circumference (-0.56 mm/week; 95% confidence interval (CI): -0.73, -0.40), abdominal circumference (-0.58 mm/week; 95% CI: -0.81, -0.34), and femur length (-0.19 mm/week; 95% CI: -0.23, -0.14). This reduced growth resulted in a smaller femur length from midpregnancy (gestational age 18-24 weeks) onwards and smaller head and abdominal circumferences from late pregnancy (gestational age >= 25 weeks) onwards. Analyses using standard deviation scores for the growth characteristics demonstrated the largest effect estimates for femur length. The authors concluded that maternal smoking during pregnancy is associated with reduced growth in fetal head circumference, abdominal circumference, and femur length. The larger effect on femur length suggests that smoking during pregnancy affects primarily peripheral tissues.