Women prone to the potentially fatal condition pre-eclampsia are less at risk if they change partner before becoming pregnant again, say experts.

But women with no history of the condition increase their risk by almost a third if they become pregnant by a new partner.

Dr De-Kun Li, based at the Kaiser Foundation Research Institute in Oakland, California, looked at 140,147 women in the state who had given birth twice.

Approximately two per cent of them reported pre-eclampsia in the first birth, and just under one per cent in the second.

However, those who had the condition in the first pregnancy and then changed partners between births were 30% less likely to develop the disorder than those who remained with one partner.

Blood pressure rise

Dr Li said: "If you never had a history of pre-eclampsia, changing partners doesn't do you any good - in fact, it actually increases your risk a little bit."

Pre-eclampsia is caused when the woman's blood pressure increases sharply during the final weeks of pregnancy.

Not only can the pressure starve the foetus of oxygen, the condition, if left untreated, can develop into eclampsia, which can cause the mother to have fits, and can prove fatal.

Usually the woman is placed under close observation - the child can be delivered early if the condition worsens.

The authors of this study, which was published in the American Journal of Epidemiology, suggest that the increased risk may be linked to both mother and father in pre-eclampsia cases having high levels of a particular protein.

"Basically, you and your partner are too similar in some ways," said Dr Li, "but we don't know why.