Stopping smoking — even in the first weeks of a pregnancy — appears to avert many of the adverse effects of tobacco on the fetus, researchers reported.
In a prospective cohort analysis, women who stopped smoking when they found they were pregnant had babies that were similar in size to those of women who had never smoked, according to Nick Macklon, MD, and colleagues at the University of Southampton in Southampton, England.
A similar effect was observed for head size and gestational age at birth, Macklon reported at the annual meeting of the European Society of Human Reproduction and Embryology in Stockholm.
“We can now give couples hard evidence that making the effort to stop smoking in the periconceptional period will be beneficial for their baby,” Macklon said in a statement.
The finding comes from an analysis of more than 50,000 pregnancies and births at the University of Southampton medical center between 2002 and 2010, Macklon reported.
Low birthweight is the most common negative outcome of smoking during pregnancy, Macklon and colleagues noted, although other adverse effects are also possible, including prematurity.
For this analysis, the researchers analyzed clinical, lifestyle and socioeconomic data and, in particular, information on smoking habits, he reported, and looked for associations with birthweight, head circumference, and gestational age at birth.
Women in the study were divided into seven groups, according to their smoking status, and analysis showed that: 52% of the women said they had never smoked. 14.2% had stopped more than a year before the pregnancy. 6.8% had stopped during the year before conceiving. 8.3% stopped when they had the pregnancy confirmed.
The remaining women smoked during the pregnancy, including 10.9% of the total who reported smoking up to 10 cigarettes a day, 7.2% who smoked from 10 through 20 a day, and 0.8% who smoked more than 20 a day.
In a univariate analysis, the average birthweight of babies born to never-smokers was 3.43 kilograms, or about 7.56 pounds, Macklon reported.
In comparison, women who stopped smoking after they learned they were pregnant had babies that weighed 3.45 kilograms on average.
As well, those who stopped a more than or less than a year before pregnancy had babies whose average birthweight was 3.50 and 3.45 kilograms, respectively.
On the other hand, among the smokers, the average birthweight was 3.24 kilograms in those smoking up to 10 cigarettes day, 3.17 kilograms in those smoke 10 through a day, and 3.11 in women who smoked more than 20 a day, Macklon reported.
After adjusting for such things as gestational age, mother’s age, body mass index, and socioeconomic class, the dose-dependent effect remained significant ( P <0.05), he reported.
A similar pattern was seen for head circumference and the risk of prematurity, he added.
“We hope that our research will provide additional encouragement to mothers-to-be to give up cigarettes,” Macklon said.
The researchers did not report any external support for the study or any financial conflicts.