For pregnant women who smoked cigarettes prior to pregnancy, smoking cessation at the start of or during pregnancy was associated with a reduced risk for preterm birth, according to research published in JAMA Network Open.
Data from birth certificates were collected for 25,233,503 women who delivered live neonates and had known prepregnancy and trimester-specific smoking frequency data recorded on the birth certificate. Women were included in the study if they had smoked ≥1 cigarette during the 3 months leading up to pregnancy. The primary outcome measure was cigarette smoking cessation throughout pregnancy (ie, no smoking during any trimester). The second outcome was cigarette smoking cessation after the end of the first trimester, and the third outcome was cigarette smoking cessation after the second trimester. The fourth outcome was cigarette smoking cessation during the third trimester, and the final outcome was preterm birth.
Socioeconomic characteristics of expectant mothers as well as pregnancy history were recorded. Smoking frequency was categorized as 0, 1 to 9, 10 to 19, and ≥20 cigarettes per day in the 3 months before pregnancy or during the first, second, and third trimesters.
The proportion of prepregnancy smokers who quit throughout pregnancy was 24.3% in 2011 and 24.6% in 2017. The proportion of prepregnancy smokers who quit during the third trimester was 39.5% in 2011 and 39.7% in 2017. High-frequency cigarette smoking was a common occurrence during all 3 trimesters; for example, 46.9% of women who smoked during the third trimester smoked ≥10 cigarettes per day. The proportion of preterm births increased with smoking frequency in each trimester.
Among expectant mothers who smoked prior to pregnancy, the odds of preterm birth were higher for those age ≤15 years. Increased frequency of smoking during the first and second trimesters was associated with increased odds of preterm birth. Conversely, the odds of preterm birth decreased the earlier smoking cessation occurred in pregnancy.
Of note, the odds of preterm birth were higher for non-Hispanic black expectant mothers who did not smoke prior to or during pregnancy than for non-Hispanic white expectant mothers who smoked 1 to 9 cigarettes per day and throughout pregnancy.
“Cigarette smoking cessation may be especially difficult for pregnant women,” the authors concluded. “However, quitting — and quitting early in pregnancy — was associated with reduced risk of preterm birth even for high-frequency cigarette smokers.”
Soneji S, Beltrán-Sánchez H. Association of maternal cigarette smoking and smoking cessation with preterm birth. JAMA Netw Open. 2019;2(4):e192514.