The impact of maternal smoking on fetal and infant growth

Background: Low birth weight is associated with accelerated postnatal growth and adverse adult health outcomes. Maternal smoking is a major risk factor for low birth weight. This study aims to assess: •Pre- and postnatal growth associated with maternal smoking compared to other risk factors for low birth weight.•The effect of reduction of maternal smoking on growth. Subjects: A cohort (n=269) followed with ultrasound measurements in the third trimester and postnatal anthropometric measurements until 6 months of age. Mothers were interviewed about their smoking habits at 18 and 28 weeks of pregnancy. Results: Maternal smoking was associated with a greater reduction in birth length SDS than other causes of equally reduced birth weight (mean difference: −0.25 SDS, P=0.013). The adjustment of gestational age, based on bi-parietal diameter at an early dating scan, indicated that mothers who reduced smoking carried smaller fetuses than mothers who continued to smoke heavily (mean difference=2.6 days, P=0.012). Birth weights in these two groups were similar (P=0.87). However at 3 months of age, reduced smoking was associated with lower weight (mean difference=−0.38 SDS, P=0.045). Conclusions: Maternal smoking was associated with a reduction of linear growth, which was more marked than that of other risk factors, and which seemed to occur before the 3rd trimester. The results indicated a beneficial effect of reduction of smoking upon third trimester growth, and that the decision to reduce smoking in mid-pregnancy may be influenced by early fetal size.