LOS ANGELES — A pregnant smoker who cuts back just one cigarette a day in her third trimester can hope to increase her newborn's birth weight by24 g, according to a prospective study reported at the annual meeting of the Society for Gynecologic Investigation.
“The message is, Keep at 'em. Don't stop trying to get women to reduce their smoking volume,” said Ira M. Bernstein, M.D., who presented data on 160 women and their offspring.
The mothers were enrolled in a randomized, prospective trial of a voucher system designed to help pregnant women stop smoking or stay cigarette free. Dr. Bernstein of the University of Vermont, Burlington, said investigators determined a woman's smoking volume by a combination of self-reports, and measurement of urinary cotinine and exhaled carbon monoxide.
Before pregnancy, the group averaged 18.2 cigarettes a day. They had already cut down to 6.7 cigarettes per day by the time they enrolled in the study, which was at 12 weeks' gestation on average. By 28 weeks, they were down to 4.8 cigarettes daily.
All had singleton pregnancies with a mean birth weight of 3,266 g. The mean gestational age at delivery was 38.6 weeks, with 17 babies born preterm. Stepwise multivariate regression analysis found smoking in the third trimester accounted for 10% of variance in birth weight. Dr. Bernstein reported a linear relationship in which babies weighed 24 g less at birth for every cigarette their mothers smoked per day in the third trimester.
“The literature is mixed. Some data say the first trimester is critical. These data support that the third trimester is more important,” he said.
The National Institutes of Health and a General Clinical Research Center grant supported the study.