For Pregnant Smokers, Early Quitting Linked to Lower Preterm Birth Risk

Hiram Beltrán-Sánchez, PhD

For expectant parents who smoke, quitting before pregnancy or as early as possible during pregnancy reduces the risk of preterm birth.

A study of smoking cessation before or during pregnancy found that the likelihood of preterm birth (less than 37 weeks of gestation) was reduced more the earlier an expectant parent quit smoking during pregnancy. However, the research also showed that just under a quarter of those who smoked before pregnancy quit entirely during pregnancy, which reflects the challenges of quitting smoking during pregnancy.

Study investigators Samir Soneji, PhD, Dartmouth Geisel School of Medicine, Lebanon, New Hampshire, and Hiram Beltrán-Sánchez, PhD, of the University of California, Los Angeles, said the results showed that the risk of preterm birth was associated with when and whether the expectant parent quit smoking.

“Our national study found a dose-response—type association among women who smoked before pregnancy: the risk of preterm birth was highest among those who smoked throughout pregnancy, lower for those who quit after the first trimester, and still lower for those who quit throughout pregnancy,” wrote Soneji and Beltrán-Sánchez.

The authors noted, however, that the risk of preterm birth was still higher for prepregnancy smokers—those who smoked in the 3 months before pregnancy—but quit throughout pregnancy than those who were not prepregnancy smokers.

The cross-sectional study analyzed data from 25,233,503 expectant parents who delivered live infants and had available data on cigarette smoking frequency before and during pregnancy. Data was pulled from live birth certificates from 2011 to 2017.

The modal age of parents at delivery was 25-29 years; 52.9% were non-Hispanic white, 23.6% were Hispanic, and 14.2% were non-Hispanic black. A large majority of parents (89.6%) did not smoke in the 3 months before pregnancy while 10.4% did report smoking during that time.

The proportion of prepregnancy smokers who quit throughout pregnancy was 24.3% in 2011 and 24.6% in 2017. The proportions of those who quit during pregnancy in 2011 and 2017, respectively, were 14.5% and 14.4% during the first trimester, 6.7% and 6.8% during the second trimester, and 39.5% and 39.7% during the third trimester.

The investigators shared an example of the effect of quitting smoking at various points for 25- to 29-year-old, non-Hispanic white, first-time pregnant smokers who used 1-9 cigarettes each day before pregnancy. If that smoking rate continued throughout pregnancy, the probability for preterm birth was 9.8% (95% Confidence Interval [CI], 9.7%-10.0%), but this decreased to 9.0% (95% CI, 8.8%-9.1%) if smoking cessation began at the start of the second trimester (an 8.9% relative decrease). If they quit smoking by the start of pregnancy, the probability of preterm birth dropped to 7.8% (95% CI, 7.7%-8.0%)—a relative decrease of 20.3%.

The investigators noted that smoking rates and cessation were self-reported and that birth certificate data do not include information about alcohol use or secondhand smoke exposure during pregnancy.

“Expectant mothers who smoke may face greater challenges in quitting compared with their counterparts who are not pregnant,” wrote Soneji and Beltrán-Sánchez.

They noted that nicotine withdrawal symptoms arise sooner during pregnancy than they do in non-pregnant smokers. Additionally, due to a lack of research in pharmacotherapy for smoking cessation in pregnant participants, there are limited options for nicotine replacement therapy during pregnancy.

Soneji and Beltrán-Sánchez concluded that cigarette smoking remains a public health burden during pregnancy in the United States.

The study, “Association of Maternal Cigarette Smoking and Smoking Cessation With Preterm Birth,” was published in JAMA Network Open.