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Large study finds no evidence of increased risk of major birth defects

Quitting smoking during pregnancy greatly benefits both the mother and baby. Nicotine replacement therapy (NRT), varenicline, and bupropion are common quit-smoking medicines, but we do not know whether they are safe to use during pregnancy. A new study, published in , analysing health data from Australia, New Zealand, Norway, and Sweden showed no increase in the risk of any major birth defects in babies of women who used these medicines in early pregnancy compared to babies of women who smoked but did not use a quit-smoking medicine. This study also showed no differences in birth defects in specific body system following the use of NRT or varenicline. These findings provide assurance for pregnant women and health care providers considering the use of quit-smoking medicines.

How did we conduct this research?

We analysed multiple sources of health data from women who gave birth between 2001 and 2020 in New South Wales Australia, New Zealand, Norway, and Sweden. We calculated the rates of major birth defects—both overall and in specific body systems—among babies of women who used a prescription NRT, varenicline, or bupropion in the first 13 weeks of pregnancy. These rates were compared to those among babies born to women who smoked during early pregnancy but did not use a prescribed quit-smoking medicine. We analysed the data for each country separately and combined the results.

What did we find?

The study included 9325, 3031 and 1042 babies of women who used NRT, varenicline and bupropion in in the first 13 weeks of pregnancy, respectively. Compared to babies of women who smoked during early pregnancy without using a quit-smoking medicine, we found no differences in the overall rates of major birth defects for NRT (3.76% vs 3.44%), varenicline (3.27% vs 3.66%), or bupropion (3.55% vs 3.88%). When examining birth defects in specific body systems among babies of women using NRT, there were no significant differences in defects of the heart, limbs, genital organs, kidney and urinary tract, respiratory system, digestive organs or clefts. Similarly, the use of varenicline showed no differences for defects of the heart, limbs, genital organs, or kidney and urinary tract. For bupropion, the low number of women using the medicine made it impossible to draw conclusions about specific birth defects.

What do our findings mean?

Given the damaging effects of smoking during pregnancy, it is reassuring that we found no clear increase in the risk of birth defects following the use of NRT and varenicline in early pregnancy. This new evidence can help pregnant women who smoke, along with their healthcare providers, make informed decisions about using quit-smoking medicines during pregnancy.