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Pregnant? Quitting Smoking Early Matters

Rates of preterm delivery and small-for-gestational-age babies were similar in women who quit smoking before 15 weeks’ gestation and in nonsmokers.

Maternal smoking has been associated with higher rates of preterm births and small-for-gestational-age (SGA) babies; however, whether quitting smoking early during pregnancy can diminish these adverse outcomes is unknown. In a prospective study of 2500 nulliparous women in New Zealand and Australia, investigators assessed pregnancy outcomes in three cohorts based on self-reported smoking status: women who did not smoke during pregnancy (nonsmokers; 1992), women who stopped smoking before 15 weeks’ gestation (stopped smokers; 261), and current smokers (251).

Rates of spontaneous preterm deliveries and births of SGA infants were similar for stopped smokers and nonsmokers. Current smokers had higher rates of preterm deliveries and SGA infants than stopped smokers (10% vs. 4%; P=0.006, and 17% vs. 10%; P=0.03, respectively). In an analysis adjusted for potential demographic and clinical risk factors, current smokers still had a threefold higher likelihood of preterm deliveries and almost double the risk for SGA infants compared with stopped smokers. Mean scores for stress, anxiety, and depression (secondary outcomes) did not differ between current and stopped smokers.

Comment: Half the stopped smokers in this study quit before 6 weeks’ gestation, probably when they discovered that they were pregnant. Current smokers might have underreported their status: Half admitted to smoking only 1 to 5 cigarettes daily, whereas only 20% claimed to smoke more than 10 cigarettes daily. Nonetheless, the threefold higher risk for preterm delivery among smokers is well worth keeping in mind as we counsel them about the benefits of putting down the cigarettes: Even women who quit as late as 32 weeks’ gestation had better pregnancy outcomes than those who did not quit (JAMA 1993; 269:1519).

— Wendy S. Biggs, MD

Published in Journal Watch Women's Health April 9, 2009

Citation(s):

McCowan LME et al. Spontaneous preterm birth and small for gestational age infants in women who stop smoking early in pregnancy: Prospective cohort study. BMJ 2009 Mar 26; 338:b1081. (http://dx.doi.org/10.1136/bmj.b1081)

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