Around 10% of pregnant women suffer from pre-eclampsia, a condition in which high blood pressure can lead to injury or even death in the mother and the foetus.

Women can try to reduce their blood pressure by resting or with medication. But drugs may put the foetus at risk, and sometimes even the maximum dose fails to get blood pressure down.

New Scientist magazine reports that a team from Umea University in Sweden have discovered that breathing problems that cause snoring may be a risk factor.

Dr Karl Franklin and colleagues gave questionnaires to 502 pregnant women.

While only 4% reported frequent snoring before pregnancy, 23% snored by the end of their pregnancies.

Around 10% of the snoring women had pre-eclampsia, while only 4% of non-snorers developed the condition.

All patients with pre-eclampsia started snoring before any hint of pre-eclampsia, such as blurred vision, appeared.

Similar findings

High blood pressure can kill

A second study by the University of Sydney produced similar findings.

Dr Natalie Edwards and her colleagues at the University of Sydney looked at 32 women with severe pre-eclampsia and 40 with normal pregnancies and found that all the women with pre-eclampsia were snorers.

Women with the highest degree of airway obstruction during sleep also had the highest blood pressures.

The Australian researchers found that they could prevent both the snoring and the high blood pressure by giving women breathing masks attached to a machine that kept their airways open while they were asleep.

Dr Edwards said: "All of the obstetricians were impressed that we could control this so effectively."

Lincolnshire GP Dr Martyn Walling, a member of the Primary Care Gynaecology Group, said there was no obvious medical link between snoring and pregnancy.

He said: "Snoring can be more common in pregnancy because women who are 30-40 weeks pregnant can find it uncomfortable to sleep on their side, and have to start sleeping on their back."