Stopping Smoking Early in Pregnancy Cuts Risk of Preterm Birth

Smoking cessation during pregnancy, especially in the first trimester, was associated with a decreased risk for preterm birth, an analysis of over 25 million live births found.

In a light-smoking, 25-to 29-year-old white woman, for example, the probability of a preterm birth was 9.8% if she continued smoking throughout her pregnancy but dropped to 7.8% if she quit smoking at the start of her pregnancy (20.3% relative decrease), reported Samir Soneji, PhD, of Dartmouth Geisel School of Medicine in Lebanon, New Hampshire, and colleagues.

If these mothers-to-be stopped smoking at the start of the second trimester, the probability of preterm birth was 9.0% (8.9% relative decrease), they wrote in JAMA Network Open.

"We know that nationally the number of women who have started pregnancy as smokers has decreased substantially, and that is good news," said Soneji. "One concern in our findings, though, is that there doesn't seem to be much progress in getting women to quit when they begin their pregnancies as smokers."

As noted, the percentage of pre-pregnancy smokers who quit for their entire pregnancy did not change significantly during the period studied, 24.3% in 2011 and 24.6% in 2017. Meanwhile, 14.5% of women in 2011 and 14.4% in 2017 quit after the first trimester and 39.5% and 39.7%, respectively, quit during the third trimester.

Although the study didn't examine the reasons for this, Soneji told MedPage Today that smoking cessation may not be high on the list of issues during prenatal visits, and, if it is brought up, pregnant smokers may not be offered smoking cessation treatments that have been shown to increase the chances for success, such as nicotine replacement therapy or pharmacotherapies like varenicline.

The U.S. Preventive Services Task Force recommends behavioral modifications for smoking cessation during pregnancy, concluding that the evidence on pharmacotherapy and electronic nicotine delivery systems for smoking cessation during pregnancy is insufficient.

It has been left to the provider to determine whether to offer these interventions, Soneji said, adding that discussing smoking cessation with pregnant patients and offering treatment is critical.

"If an expectant mom says she is willing to quit, she should be given all the support available," he said.

Overall, among women, the CDC estimates that 16.5% were current smokers in 2011, which dropped to 12.2% in 2017. And even though smoking prevalence among expectant mothers has declined, a recent analysis found that in 2016, 7.2% of pregnant women in the U.S. -- or 283,000 women -- continued to smoke during pregnancy.

In the newly published study, Soneji and colleagues analyzed birth certificate data collected by the U.S. National Center for Health Statistics as part of the National Vital Statistics System. Since 2003, information on maternal smoking frequency 3 months prior to pregnancy has been collected, as well as data on trimester-specific smoking frequency. This revision had been adopted by all U.S. states by 2016.

Among the 25,233,503 expectant mothers who delivered live children from 2011 to 2017, 52.9% were white, 23.6% were Hispanic, and 14.2% were black. A total of 2,633,307 smoked during the 3 months prior to pregnancy. High-frequency cigarette smoking (≥10 cigarettes daily) was common among expectant mothers who smoked during pregnancy (46.9% of third-trimester smokers smoked ≥ 10 cigarettes per day in 2017).

"Cigarette smoking continues to represent a public health burden for women during pregnancy," the researchers concluded. "Cigarette smoking cessation may be especially difficult for pregnant women. However, quitting -- and quitting early in pregnancy -- was associated with reduced risk of preterm birth even for high-frequency cigarette smokers."