Comparison of cotinine levels in pregnant women while smoking and when using nicotine replacement therapy

Nicotine replacement therapy (NRT) helps smokers quit smoking, but trials indicate that there is no evidence that it is effective during pregnancy. As metabolism increases during pregnancy, NRT may deliver insufficient nicotine to alleviate withdrawal symptoms. There is mixed evidence as to what levels of cotinine are reached from nicotine exposure during pregnancy while using NRT compared with smoking.

We analyzed data on 33 pregnant participants from the NRT arm of a randomized control trial who had stopped smoking and were still using 15 mg/16 hr nicotine patches 1 month after quitting. Salivary cotinine levels when smoking at baseline were compared with levels on NRT at 1 month using the Wilcoxon test.

Cotinine levels were a median of 98.5 ng/ml while smoking and 62.8 ng/ml while using NRT and remaining abstinent (p = .045). Participants with the highest cotinine measurements when smoking also tended to have the steepest reduction in cotinine levels while using NRT. This was most noticeable among participants with baseline cotinine levels more than 150 ng/ml (n = 9) who had a greater reduction in median cotinine levels (median difference -134.8 ng /ml [95% CI = -144.5 to -125.9]) than those with a baseline cotinine level under 150 ng/ml (n = 24; median difference -27.9 ng/ml [95% CI = -49.35 to -1.75]).

In a pragmatic trial that replicated clinical practice, cotinine levels generated using NRT during pregnancy were lower than levels achieved from smoking. Although the sample size of this study was small, our findings are significant and are consistent with the hypothesis that NRT patches deliver an inadequate dose of nicotine to aid smoking cessation during pregnancy.