Pregnant women who stop smoking before the 15th week have rates of preterm birth and small-for-dates babies comparable to those of non-smoking women, new research indicates. The findings show that "these severe adverse effects of smoking may be reversible if smoking is stopped early in pregnancy," Dr. Lesley M. E. McCowan, from the University of Adelaide, Australia, and colleagues comment in the British Medical Journal.

The results come from an analysis of data for 2500 women who were having their first baby. At 15 weeks' gestation, the women were classified as non-smokers, stopped smokers, or current smokers. Overall, 80 percent of the women were non-smokers, 10 percent were stopped smokers, and 10 percent were current smokers, according to the report.

The rate of preterm birth was 4 percent and the rate of babies born small-for-dates was 10 percent, among both the stopped smokers and the non-smokers. Current smokers, by contrast, had a 10 percent rate of preterm birth and a 17 percent rate of small-for-dates babies -- both significantly higher than the rates seen in the other groups.

"Maternity care providers should strive to assist pregnant women who smoke to stop early in pregnancy, emphasizing the major health benefits if they cease to smoke before 15 weeks' gestation," the team concludes.