Nicotine replacement therapy (NRT) has been successful in helping some nonpregnant women to stop smoking. NRT may be preferable to smoking during pregnancy because it contains only one of the toxic substances of tobacco smoke. However, the fetal effects of NRT are unknown and there are few data on the safety of NRT in pregnant women.
This prospective population-based cohort study examined the association between NRT use during pregnancy and the risk of stillbirth in 87,032 singleton pregnancies of women enrolled in the Danish National Birth Cohort. Categories analyzed were nonsmoker, ex-smoker, ≤10 gm tobacco/day, and >10 gm tobacco/day. Stillbirth was defined as any nonbreathing fetus showing no signs of life at birth after a minimum of 22 weeks gestation. The unadjusted and adjusted hazard (HR) ratios were estimated using Cox proportional hazards and multivariate regression models.
Of the 2% of women who had used NRT during pregnancy, 56% had continued to smoke during pregnancy, while 30% had stopped smoking for the duration of the pregnancy and 14% had quit smoking. A total of 495 of the 87,032 pregnancies (5.7 per 1000 births) ended in stillbirth. Among NRT users, the rate of stillbirth was 4.2 in 1000 births. Compared to nonusers, women using NRT had an unadjusted HR of 0.75 (95% CI 0.37-1.15) for stillbirth. The risk of stillbirth was not affected by the type of NRT used (patches only, chewing gum only, inhaling substances only, and various combinations of NRT products). Adjustment for smoking habits during pregnancy lowered the estimated risk, while adjustment for household socio-occupational status and maternal age did not change the estimate. Consistent with previous studies, the risk of stillbirth was increased during pregnancy among smokers who did not use NRT (HR 1.46, 95% CI 1.17-1.82). Women who both smoked and used NRT during pregnancy had a HR of 0.83 (95% CI 0.34-2.00).
These findings show that the use of NRT during pregnancy did not increase the risk of stillbirth. To the authors' knowledge, this is the first study to examine this association.