Women who smoke while pregnant increase their child's risk of heart attack or stroke by up to 20 percent, a new study has found.

University of Sydney researchers said today (Wednesday, June 22) they had discovered eight-year-old children whose mothers smoked during pregnancy had lower levels of high-density lipoprotein cholesterol (HDL), known to arm the body against heart disease.

The study found the children born to mothers who smoked while they were pregnant had HDL cholesterol levels of about 1.3 millimoles per litre (mmol/L), compared to the more normal level of 1.5 mmol/L in children whose mothers had not smoked.

Lead author, David Celermajer, Scandrett Professor of Cardiology at the University of Sydney said that equated to a 20 percent drop in the protective cholesterol.

"It also increases their risk of having a heart attack or stroke by 15 to 20 per cent," he said.

Professor Celermajer said the effect came after the researchers took into account other risk factors, such as whether children were exposed to cigarette smoke after birth, lack of exercise and weight.

This suggested prenatal exposure had the most impact on a child's development and left and "imprint in the womb" that had an effect later in life of increasing the risk of heart attack or stroke.

Dr Julian Ayer, a principal study researcher, of Sydney Medical School said previous research had shown links between smoking and high cholesterol levels. However, until now it had been unclear what effect exposure in the womb to cigarette smoke had on the risk of future cardiovascular disease.

"Studies show it does seem to follow that pattern through the life course," he said.

Professor Celermajer said the research had shown the imprinting lasted until age eight and the study would continue at least until the children turned 12, to see what the impacts were when the children hit puberty.

Dr Ayer said smoking during pregnancy was "still, unfortunately quite high", with about 15 per cent of Western pregnant women keeping up the habit.

The study, published in the European Society of Cardiology's European Heart Journal online today, involved 405 Sydney children born in 1997 and 1999 and began when they were still in the womb.

Data was collected before and after birth, including information on mothers' smoking habits before and after pregnancy, children's exposure to passive smoking, and height, weight, waist circumference and blood pressure measurements.

Ultrasound scans were used to measure arterial wall thickness and they took blood from 328 children to measure lipoprotein levels.

The HDL findings came this year when they took blood samples from 328 of those children.

Although smoking had no effect on the thickness of the children's arterial wall, the difference on HDL cholesterol levels attributable to mothers' smoking was about 0.15 mmol/L

Dr Ayer said although the number of children used in the study was significant, and although the subjects were from Sydney the results could be applied to any children in the West.

Professor Celermajer added: "Children born to mothers who have smoked during pregnancy will need
to be watched particularly carefully for other coronary risk factors such as high blood pressure, 'bad' cholesterol (LDL) levels, and especially cigarette smoking themselves."

The European Heart Journal is the flagship journal of the European Society of Cardiology (http://www.escardio.org [2]). It is published on behalf of the ESC by Oxford Journals, a division of Oxford University Press.