Women with a dangerous pregnancy complication have a higher risk of going on to suffer blood clots, researchers have found.
Pre-eclampsia can occur in late pregnancy
Pre-eclampsia, which only occurs in late pregnancy, causes a pregnant woman's blood pressure to rise to very high levels.
It can be dangerous for both the mother and her developing baby.
Blood clots, or venous thromboembolism, generally form in the leg. If they move to the lungs, they can prove fatal.
Canadian researchers compared 12,849 women admitted to hospital with pre-eclampsia during pregnancy with 284,188 women with other common obstetrical diseases.
You might have a predisposition, but we think there are other factors that affect clotting
Dr Dilys Freeman, University of Glasgow
All were followed up for up to three years after their discharge from hospital.
They found women who have pre-eclampsia were twice as likely to be admitted to hospital with venous thromboembolism during the observation period than women in the other group.
The researchers, from Ottowa Health Research Institute, said the absolute risk to women with pre-eclampsia was not high enough that they needed to be given medication to prevent clots.
But they said women with the condition should be checked for indications of venous thromboembolism.
Writing in the British Medical Journal, the research team led by Dr Carl van Walraven, said: "Women with pre-eclampsia have a small but significantly higher risk of subsequent venous thromboembolic disease compared with women diagnosed with other common obstetrical disease.
Dr Dilys Freeman, a specialist in vascular biology at the University of Glasgow, said some people had an inherited tendency to clot.
"If you have that, you're more likely to get pre-eclampsia. Part of what goes wrong is that clots develop in the arteries going to the placenta."
Dr Freeman agreed women who did develop pre-eclampsia were then more likely to have blood clots later in life.
But she said the risk was still low because pre-eclampsia was relatively rare, affecting a maximum of 10% of pregnancies.
Dr Freeman is leading a study looking at what other factors contribute to people developing pre-eclampsia.
"You might have a predisposition, but we think there are other factors that affect clotting.
"We are looking at micro-particles, tissue fragments from the placenta, which might form a surface on which the clots can form."