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    Original Investigation
    Obstetrics and Gynecology
    April 19, 2019

    Association of Maternal Cigarette Smoking and Smoking Cessation With Preterm Birth

    Author Affiliations
    • 1The Dartmouth Institute for Health Policy & Clinical Practice, Dartmouth Geisel School of Medicine, Lebanon, New Hampshire
    • 2Dartmouth-Hitchcock Norris Cotton Cancer Center, Dartmouth Geisel School of Medicine, Lebanon, New Hampshire
    • 3Department of Community Health Sciences, University of California, Los Angeles
    • 4California Center for Population Research, Los Angeles
    JAMA Netw Open. 2019;2(4):e192514. doi:10.1001/jamanetworkopen.2019.2514
    Key Points español 中文 (chinese)

    Question  Does an association exist between maternal cigarette smoking cessation during pregnancy and risk of preterm birth?

    Findings  In this cross-sectional study of more than 25 million pregnant women, only approximately 1 of 4 women who smoked prior to pregnancy quit throughout pregnancy, and approximately 1 of 2 women who smoked during their pregnancy smoked 10 or more cigarettes per day. Cigarette smoking cessation, especially early in pregnancy, was associated with reduced risk of preterm birth (relative decrease up to 20%) even for high-frequency cigarette smokers.

    Meaning  Greater emphasis on smoking cessation among expectant mothers who smoke may be associated with a lower burden of preterm birth.

    Abstract

    Importance  Cigarette smoking during pregnancy increases the risk of preterm birth, low birth weight, and infant mortality.

    Objective  To assess the probability of preterm birth among expectant mothers who smoked cigarettes before pregnancy and quit smoking at the start or during pregnancy.

    Design, Setting, and Participants  This cross-sectional study analyzed information provided on live birth certificates from 2011 through 2017 that were obtained from US states that implemented the 2003 revision of the US live birth certificate. In total, 25 233 503 expectant mothers who delivered live neonates and had known prepregnancy and trimester-specific cigarette smoking frequency were included in the analyses.

    Exposures  Cigarette smoking frequency (1-9, 10-19, and ≥20 cigarettes per day) 3 months prior to pregnancy and for each trimester during pregnancy.

    Main Outcomes and Measures  Cigarette smoking cessation throughout pregnancy, after the first trimester, after the second trimester, and during the third trimester irrespective of first and second trimester smoking. Probability of preterm birth (<37 weeks’ gestation).

    Results  Of 25 233 503 expectant mothers who delivered live neonates between 2011 and 2017, the modal age at delivery was 25 to 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 during the 3 months prior to pregnancy, and 2 633 307 smoked during the 3 months prior to pregnancy. 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 often occurred among expectant mothers who smoked during pregnancy (eg, 46.9% of third-trimester smokers smoked ≥10 cigarettes per day in 2017). The probability of preterm birth decreased more the earlier smoking cessation occurred in pregnancy. For example, the probability of preterm birth was 9.8% (95% CI, 9.7%-10.0%) among 25- to 29-year-old, non-Hispanic white, primigravida and primiparous expectant mothers (ie, pregnant for the first time and not yet delivered) who smoked 1 to 9 cigarettes per day prior to pregnancy and maintained this frequency throughout their pregnancy. The probability of preterm birth was 9.0% (95% CI, 8.8%-9.1%) if smoking cessation occurred at the start of the second trimester (an 8.9% relative decrease), and 7.8% (95% CI, 7.7%-8.0%) if cessation occurred at the start of pregnancy (a 20.3% relative decrease).

    Conclusions and Relevance  Quitting smoking—and quitting early in pregnancy—was associated with reduced risk of preterm birth even for high-frequency cigarette smokers.

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