Smoking influence on early and late fetal growth

Objectives Smoking during pregnancy is a leading and modifiable risk factor for fetal growth restriction (FGR) and low birthweight (<10th centile). We studied the effects of smoking in the development of early and late FGR or low birthweight, as well as in uteroplacental and fetoplacental hemodynamics of growth-restricted fetuses. Methods Retrospective cohort study of 5,537 consecutive singleton pregnancies delivered at ≤34 + 0 (“early delivery” group, n=95) and >34 + 0 (“late delivery” group, n=5,442) weeks of gestation. Each group was divided into smokers and non-smokers. Prenatal diagnosis of FGR was based on customized fetal growth standards and fetal Doppler, and postnatal birthweight was assessed using the Olsen newborn chart. Results There were 15/95 (15.8%) and 602/5,442 (11.1%) smokers in the early and late delivery groups, respectively. In early deliveries, FGR was diagnosed in 3/15 (20%) of smokers and in 20/80 (25%) of non-smokers (p=0.68). We also found no differences in birthweights and hemodynamics. In late deliveres, FGR was detected in 30/602 (5%) smokers and 64/4,840 (1.3%) non-smokers (p<0.001). Birthweights <3rd centile and <10th centile were more common in smokers vs. non-smokers: 38/602 (6.3%) vs. 87/4,840 (1.8%) and 89/602 (14.8%) vs. 288/4,840 (6%), respectively (all p<0.01). Fetal Doppler of late FGR showed slightly higher umbilical artery resistances in smokers. Conclusions Smoking in pregnancy is associated with FGR, low birthweight and higher umbilical artery Doppler resistances after 34 weeks of gestation, but we could not confirm this association in earlier deliveries.