Quitting Smoking during Pregnancy Reduces Premature Birth Risk

A new study shows that giving up smoking early in pregnancy is associated with reduced risk of preterm birth, even for high-frequency cigarette smokers.

Researchers at the University of California, Los Angeles (UCLA; USA) and Dartmouth Geisel School of Medicine (DGSM; Lebanon, NH, USA) conducted a cross-sectional study that analyzed information received from 25,233,503 expectant mothers who delivered live neonates between 2011 and 2017 and had known pre-pregnancy and trimester-specific cigarette smoking frequency. The researchers reviewed cigarette smoking cessation throughout pregnancy and for each trimester alone, and calculated the probability of preterm birth.

Demographically, the modal age at delivery was 25-29 years; 52.9% were non-Hispanic white, 23.6% were Hispanic, and 14.2% were non-Hispanic black women; 22,600,196 mothers did not smoke three months prior to pregnancy, and 2,633,307 smoked during that period. The proportion of pre-pregnancy smokers who quit throughout pregnancy was 24.3% in 2011, and 24.6% in 2017, and the proportion of pre-pregnancy smokers who quit during the third trimester was 39.5% in 2011 and 39.7% in 2017. In addition, high-frequency cigarette smoking often occurred among those who smoked during pregnancy.

The results revealed that the probability of preterm birth decreased more the earlier smoking cessation occurred during the pregnancy. For example, the probability of preterm birth was 9.8% among 25-29 year olds, non-Hispanic white, and primigravida and primiparous expectant mothers who smoked 1-9 cigarettes per day prior to pregnancy, and maintained this frequency throughout. The probability of preterm birth was 9% if smoking cessation occurred at the start of the second trimester (an 8.9% relative decrease), and 7.8% if cessation occurred at the start of pregnancy (a 20.3% relative decrease). The study was published on April 5, 2019, in JAMA Network Open.

“Pregnancy can be a stressful time in a woman's life, and women who smoked prior to pregnancy may turn to smoking or continue to smoke as a way to mitigate this stress,” said lead author Samir Soneji, PhD, of DGSM. “Pregnancy is often a time when women have more frequent contact with the healthcare system, and this increased contact provides expectant mothers an opportunity to discuss their concerns about smoking, including their attempts to stop, and receive the support and resources they need to safely and successfully quit.”

“Even among women who smoke a pack a day or more, there can be a substantial reduction in the risk of premature births if these heavy smokers quit early in pregnancy,” concluded Dr. Soneji. “Thankfully most premature babies end up doing well, but premature birth is strongly linked to infant mortality. If we determine quitting, and quitting early, reduces the risk of infant mortality, then that may speak to mothers even more saliently about the importance of smoking cessation.”

Related Links:
University of California, Los Angeles
Dartmouth Geisel School of Medicine