Stillbirth among women prescribed nicotine replacement therapy in pregnancy: analysis of a large UK pregnancy cohort

Objective: To compare risk of stillbirth between maternal smokers and those prescribed NRT during pregnancy.\ud \ud Design: Cross-sectional analysis nested in a pregnancy cohort with longitudinal routinely-recorded medical data.\ud \ud Setting: United Kingdom primary care; The Health Improvement Network (THIN) general practice database\ud \ud Population: 220,630 singleton pregnancies ending in live or stillbirth, 2001-2012 \ud \ud Methods: Women were categorised into three groups: NRT (prescribed during pregnancy or one month before conception); smokers; controls (non-smokers without a pregnancy NRT prescription). \ud \ud Main Outcome Measure: odds ratios (OR) adjusted to maternal characteristics and 95% confidence intervals (CIs) for stillbirth\ud \ud Results: A total of 805 pregnancies ended in stillbirth (3.6/1,000 births). Absolute risks of stillbirth in NRT and smoker groups were both 5/1,000 births compared with 3.5/1,000 births in the control group. Compared with the control group, the adjusted odds of stillbirth in the NRT group was not statistically significant (OR=1.35, 95% CI 0.91-2.00), although it was similar in magnitude to that in the smokers group (OR=1.41, 95% CI 1.13-1.77).\ud \ud \ud Conclusions: We found no evidence of a statistically significant association between being prescribed NRT during pregnancy and odds of stillbirth compared with non-smoking women. Although our study had much larger numbers than any previously, an even larger study with biochemically-validated smoking outcome data and close monitoring of NRT use throughout pregnancy is required to exclude effects on findings of potential exposure misclassification