Two studies, published together on bmj.com today, add further weight to the theory that pre-eclampsia and cardiovascular diseases may share common causes or mechanisms.
The first study finds that women who have had pre-eclampsia during pregnancy have a more than two fold higher risk of heart disease in later life, while the second shows that women with cardiovascular risk factors that are present years before pregnancy may be predisposed to pre-eclampsia.
Pre-eclampsia is a serious condition where abnormally high blood pressure and other disturbances develop in the second half of pregnancy. It affects about 5% of all first-time pregnancies and is dangerous for both mother and child.
In the first study, researchers in London analysed 25 studies involving over 3 million women to calculate the future health risks of women who have had a pregnancy affected by pre-eclampsia that is likely explained by the association with heart disease.
They found a small increase in overall mortality among women who had had pre-eclampsia. Women with a history of pre-eclampsia also had an almost four fold increased risk of high blood pressure (hypertension) and a two fold increased risk of fatal and non-fatal ischaemic heart disease, stroke, and blood clots (venous thromboembolism) in later life.
They found no increase in risk of any cancer, including breast cancer, suggesting a specific relationship between pre-eclampsia and cardiovascular disease.
The authors explain that, since the risk of a cardiovascular event increases with age, and assuming that the effect of the pre-eclampsia is independent of other risk factors, absolute risk at age 50-59 years would be around 8% without and 17% with a history of pre-eclampsia and at 60-69 years the risk would be 14% without and around 30% for a woman with a history of pre-eclampsia.
This suggests that a woman with pre-eclampsia might become eligible for preventative therapies at an earlier age than would otherwise be the case.
The mechanism underlying this association remains to be defined, but whatever its nature, a history of pre-eclampsia should be considered when evaluating risk of cardiovascular disease in middle aged women, they conclude.
In the second study, researchers in Norway examined whether cardiovascular risk factors assessed before conception predict pre-eclampsia.
3,494 women were included in the analysis. Several cardiovascular risk markers, including blood pressure, cholesterol and blood sugar levels, weight, and body mass index, were recorded before pregnancy.
133 (3.8%) of these women had a pregnancy complicated by pre-eclampsia. After adjusting for factors such as smoking and social status, the odds of pre-eclampsia were seven times greater in women with high pre-pregnant blood pressure, total cholesterol and blood sugar levels compared to women with readings in the normal range.
Furthermore, a family history of high blood pressure, ischaemic heart disease, or diabetes was each associated with a doubling in risk, while overweight and obese women also had a higher risk compared to women of normal weight. Women who used oral contraceptives before pregnancy had half the risk of pre-eclampsia compared to never or previous users.
These results show that unfavourable cardiovascular risk factors that were present years before pregnancy are strong predictors of pre-eclampsia, suggesting that pre-eclampsia and cardiovascular diseases may share a common origin, say the authors.
However, this does not rule out the possibility that the pre-eclamptic process itself may also contribute to subsequent cardiovascular risk, they conclude.
An accompanying editorial says that guidelines for prevention of cardiovascular disease are appropriate for all women, while future research must investigate whether women with previous pre-eclampsia should have their cardiovascular risk markers treated earlier and more aggressively (or both).