Is the apparently protective effect of NRT used in pregnancy on infant development explained by smoking cessation in pregnancy?
Longer term outcomes of children of pregnant smokers are currently not well studied. Evidence from the Smoking, Nicotine and Pregnancy (SNAP) trial showed that children born to women randomised to use nicotine replacement therapy (NRT) in pregnancy were less likely to have developmental impairment. We hypothesised that NRT might have exerted this positive impact by encouraging smoking cessation within pregnant women using this treatment. To investigate this hypothesis, we investigate within the trial cohort, the relationship between fetal exposure to maternal smoking in pregnancy and infant developmental impairment at 2 years.
1,010 pregnant smokers aged 16 to 45 years were enrolled in the SNAP trial at 12 to 24 weeks gestation. Participants were randomized to receive up to 8 weeks supply of either nicotine patches or placebo. Validated maternal smoking status data were collected at one month after a quit date and around childbirth. At 2 years infant developmental outcomes were measured using the Ages and Stages Questionnaire (ASQ) which assesses 5 domains of childhood development – communication, gross motor, fine motor, problem solving and personal-social skills. Logistic regression models were used to compare infants’ developmental outcomes at 2 years in those born to women who smoked throughout pregnancy with those whose mothers stopped for either the first month or the whole of pregnancy. Multivariable analyses were adjusted for birth weight, maternal age, age full time education was completed, maternal BMI and partner’s smoking status.
Developmental impairment was present in 12.7% of the 2 year olds. Although smoking abstinence was achieved in 16.8% and 8.5% of these women at 1 month post-quit date and for the whole of pregnancy respectively, maternal tobacco smoking at neither exposure was associated with children’s developmental impairment at 2 years. Compared to women who smoked throughout pregnancy, the odds of developmental impairment for children born to mothers who stopped smoking for one month or until delivery were respectively (OR: 0.99, 95%CI: 0.59-1.66, p=0.96) and (OR: 1.55, 95%CI: 0.84-2.87, p=0.18). Adjustment for potential confounders did not affect findings.
Analyses did not show any association between fetal tobacco smoke exposure during pregnancy and developmental impairment in early childhood at two years and do not support the hypothesis that NRT improved SNAP trial infants’ developmental outcomes through an effect on maternal smoking.