Women who smoke during pregnancy increase their risk of developing blood clots and other problems as well as restricting the growth of their unborn children, Medical News Today reported May 2.

Researchers from the University of Sydney who compared pregnant women who smoked 10 or more cigarettes daily to nonsmokers found that the smokers were more likely to develop endothelial dysfunction, which in turn can cause dilation of blood vessels, inflammation of the vascular wall, and blood clots. The study showed that the endothelial dysfunction persisted even when the smokers were told to abstain for a period of nine hours.

Also, while none of the babies born to 20 women in the control group were underweight, significant numbers of babies had low birth weights for their gestational age, with a particular association to mothers who had reduced endothelial function.

"Our work provides evidence that smoking has a direct and long-term deleterious effect on vascular function in pregnancy and thus provides evidence to why babies of smokers are growth restricted," said researcher Ann Quinton.

The study was published in the May 2008 issue of BJOG: An International Journal of Obstetrics and Gynaecology.