Objective: To evaluate the impact of cotinine-confirmed smoking reduction during pregnancy on infant birth weight and gestational age at birth.
Design: Group analyses from a prospective, randomized smoking-cessation intervention trial using cotinine levels to assess smoking cessation and reduction.
Setting: Four maternity clinics of Jefferson County Health Department in Birmingham, Ala.
Patients: A total of 803 pregnant smokers and 474 never smokers with a fetal gestational age of 32 weeks or less at the first prenatal visit to a clinic.
Main outcome measures: Infant birth weight and gestational age at birth.
Results: Infants who were born to women who quit smoking (quitters) had the highest mean birth weight (3371 +/- 581 g), followed by infants who were born to women who did not change smoking behavior (no changers) (3043 +/- 587 g). The mean infant birth weight of infants born to the quitters, adjusted by mother's age, race, height, weight at baseline, and gestational age at delivery was 241 g heavier than that among the no changers (P = .0008) and 167 g heavier than the reducers (P = .04). The adjusted mean infant birth weight of infants born to the reducers was 92 g heavier than that among the no changers (P = .08). White reducers with baseline cotinine levels greater than 100 ng/mL had infants who were 241 g heavier than did white no changers. A 220-g difference was also seen in black reducers with a baseline cotinine level of 100 ng/mL or less. Although smoking cessation increased infant gestational age at delivery by 1 week, smoking reduction had little effect.
Conclusion: Cotinine-validated smoking reduction rates were positively associated with an increase in infant birth weight. While smoking cessation must continue to be the primary objective for pregnant smokers, specific intervention methods should also be directed toward smoking reduction for women who cannot quit.