Expecting mothers, take note. As smoking during pregnancy is linked with negative health outcomes, a team of researchers has found that smoking cessation during pregnancy may reduce the risk of pre-term birth.

The findings, published in the JAMA Network Open journal, showed that the probability of pre-term birth decreased with earlier smoking cessation in pregnancy — up to a 20 per cent relative decrease if cessation occurred at the beginning of pregnancy.

“Of concern, though, given the substantial benefits of smoking cessation during pregnancy is that the proportion of pre-pregnancy smokers who quit smoking during pregnancy has remained essentially stagnant since 2011,” said lead author Samir Soneji from The Dartmouth Institute for Health Policy and Clinical Practice in the US.

For the study, the researchers conducted a cross-sectional study of more than 25 million pregnant women who gave birth to live neonates during a six-year period — measuring their smoking frequency three months prior to pregnancy and for each trimester during pregnancy.

The negative health impacts of cigarette smoking during pregnancy, including low birth weight, delayed intrauterine development, pre-term birth, infant mortality, and long-term developmental delays, are well known.

But the good news is that the proportion of women who start their pregnancy as smokers has been declining in recent years, the researchers said.

However, the study also found that only about 25 per cent of women who smoked prior to pregnancy were able to quit throughout their pregnancy, and approximately 50 per cent of women who smoked during their pregnancy did so with high frequency (more than 10 cigarettes per day).

The researcher plans to look at quit rates and smoking intensity and their impact on the risk of infant mortality.

“Thankfully most premature babies end up doing well,” he said.

“But premature birth is strongly linked to infant mortality. If we determine quitting, and quitting early, reduces the risk of infant mortality, then that may speak to mothers even more saliently about the importance of smoking cessation,” he added.