File photo: Pre-eclampsia starts in the second half of pregnancy.

Pregnant women can be put at risk of the potentially fatal condition pre-eclampsia by their own baby’s DNA, a study has found.

The findings help to solve the puzzle of what causes the condition, which can affect one in 20 expectant mothers.

Researchers hope that by knowing more about the genes doctors will be able to identify mothers most at risk and that the findings will eventually lead to new treatments.

Pre-eclampsia starts in the second half of pregnancy. Early symptoms include high blood pressure and protein in the urine.

Complications include blackouts, vomiting, swollen limbs and stomach pain. In the worst cases pre-eclampsia causes organ damage and fits. The condition can be fatal to both mothers and their babies.

It was known that the condition is often inherited, but scientists have now identified genes carried by babies which cause their mothers to become ill. The baby’s DNA comes from both its mother’s and its father’s genes.

The problems originate with the placenta, which attaches the baby to the mother’s womb. The new research shows that certain genes in the baby can cause the placenta to leak.

The result is that a protein – produced in the placenta – that is meant to help the foetus grow ends up in the mother’s bloodstream. This can damage her blood vessels, and other organs, causing the heart to pump harder and increasing blood pressure.

Dr Linda Morgan, from the University of Nottingham, coordinated the five-year study, which included DNA samples contributed from Britain, Iceland, Norway and Finland.

The genes of babies whose mothers suffered pre-eclampsia were analysed and compared with babies whose mothers did not suffer the condition. The researchers identified the protein causing the damage: sFlt-1.

Dr Morgan said: "For many years midwives and obstetricians have known that a woman is more likely to develop pre-eclampsia if her mother or sister had the disorder.

"More recently research has shown that the condition also runs in the families of men who father pre-eclamptic pregnancies.

"As it is the baby’s genes that produce the placenta, we set out to see if we could find a link between the baby’s DNA and the condition.

"We found there were indeed some features in a baby’s DNA that can increase the risk of pre-eclampsia."