Maternal Smoking, Nicotine Replacement Therapy in Pregnancy and Congenital Anomalies in offspring: A Population-based Study using the United Kingdom Primary Care Data

INTRODUCTION: Smoking in pregnancy is linked to several maternal and foetal complications but the association between maternal smoking and congenital anomalies (CAs) is less clear. In 2005, licensing arrangements for nicotine replacement therapy (NRT) in the United Kingdom (UK) were broadened to aid smoking cessation in pregnancy. However, little is known about the safety of NRT use in pregnancy. Therefore, we assessed the relationship between smoking or NRT use during early pregnancy and CAs in offspring.

METHODS:  We accessed data on children born between 2001-2012, using a mother-child linked dataset of primary care records from across the UK. Mothers’ smoking status and NRT use during early pregnancy (first trimester) were identified and the risks of major CAs were calculated in children of mothers who smoked or used NRT during the first trimester compared to children of non-smoking mothers using logistic regression.

RESULTS:  Out of a total of 348,167 children, 9,782 (280/10,000) had at least one major CA. During early pregnancy 16% of mothers were classified as smokers and 0.8% as NRT users. Compared with non-smokers the adjusted odds ratios (OR) for CA in children of women classified as smokers or in those prescribed NRT when pregnant were 0.99 (99% confidence interval (CI) 0.91-1.07) and 1.23 (99% CI 0.93-1.63) respectively. There was no statistically significant association between either smoking or NRT use during pregnancy and system-specific anomalies e.g. heart: OR=1.02 (99% CI 0.89-1.17) for smoking and OR= 1.09 (99% CI 0.66-1.84) for NRT use.

CONCLUSIONS: This study with larger numbers than any previous study did not find a significant association between smoking or NRT use during pregnancy and CAs. It may be likely that no true association exists. However, it is difficult to be completely certain in the absence of adequate statistical power, for which an even larger study is required.