Pre-eclampsia and cardiovascular risk

Women who suffer from pre-eclampsia during pregnancy have double the risk of heart disease in later life, reported The Guardian . A review of studies involving more than three million women found that “women with a history of pre-eclampsia had an almost fourfold risk of high blood pressure” the newspaper said. They also had an increased risk of stroke and deep vein thrombosis. Pre-eclampsia is a complication that occurs in late pregnancy and is characterised by increased blood pressure, protein in the urine, and poor functioning of the placenta.

The newspapers suggest that such women should take precautions to protect themselves and could also be prescribed medical treatment at an earlier stage, with the Daily Mail suggesting that these women could be given cholesterol-lowering statins.

The story is based on a review which combines the results of a number of studies suggesting that there is an increased risk of cardiovascular disease in later life in women who have had pre-eclampsia. This is not surprising when the similar risk factors that may predispose an individual to both pre-eclampsia and later life cardiovascular diseases are considered. However, cardiovascular diseases cannot be attributed to one risk factor alone, and usually are affected by a combination of several risk factors, such as age, diabetes, smoking and raised cholesterol. Because of this, the risk of developing these diseases in young, otherwise healthy women remains relatively small.

Where did the story come from?

Leanne Bellamy and colleagues of Imperial College London, University College London and the London School of Hygiene and Tropical Medicine carried out this research. Funding was provided by Department of Health’s National Institute for Health Research Biomedical Research Centre at University College London. It was published in the peer-reviewed British Medical Journal.

What kind of scientific study was this?

This was a systematic review combining the results of a number of studies that followed women over a period of time (cohort studies) to assess their future risks of cardiovascular disease, cancer or death after they had suffered from pre-eclampsia in pregnancy.

The researchers searched medical literature databases to look for articles published up until 2006 that described cohort studies comparing events in women with any severity of pre-eclampsia with women who did not suffer from the condition during pregnancy. They looked at results including high blood pressure (hypertension), heart disease (angina, heart attacks and heart failure), stroke, cancer (breast cancer in particular), deep vein thrombosis, and total deaths, that developed more than three months after birth.

The researchers assessed the extent of differences between the studies (e.g. study methods and characteristics of women studied) and combined these results to provide overall risk values. Of all the studies identified by the search, 25 were considered suitable for use in the analysis, and together these studies included more than 3.4 million women.

What were the results of the study?

Thirteen of the studies looked at high blood pressure, and the combined results of these studies showed that women with pre-eclampsia had nearly four times the risk of developing chronic high blood pressure during the studies’ follow-up periods (which averaged 14 years) than women who did not have pre-eclampsia. The combined results of eight studies that examined the risks of heart disease (over an average follow up of 12 years) showed that having had pre-eclampsia was associated with just over double the risk compared with women without pre-eclampsia.

Risk of both stroke (in 10½ years of follow up from four studies), and deep vein thrombosis (in 4½ years of follow up from three studies) were nearly doubled. There was also a slightly increased risk of death from any cause in the five studies that looked at this. Risks for high blood pressure and heart disease tended to increase with the number of children that the woman had had previously. For blood pressure and stroke, risks were higher the earlier in the pregnancy that the pre-eclampsia developed. Pre-eclampsia was not associated with an increased risk of developing cancer.

What interpretations did the researchers draw from these results?

The authors concluded that there is increased risk of cardiovascular diseases such as high blood pressure, stroke and heart disease in women who suffered from pre-eclampsia during pregnancy. This, they say, may explain the small increase in overall risk of death that was seen. Although the reason for these increases is not completely understood, it is possible that this is due to both pre-eclampsia and cardiovascular diseases having common causes and predispositions. The authors suggest that “a history of pre-eclampsia should be considered in the evaluation of women’s risk of cardiovascular disease”.

What does the NHS Knowledge Service make of this study?

This is a large and reliable review, combining the results of a number of studies and does suggest there to be an increased risk of cardiovascular disease in later life in women who have had pre-eclampsia. The possible reasons for the associations and the limitations to the research findings have been acknowledged by the authors.

• Although the risk of heart disease, high blood pressure and stroke was found to be increased, the actual size of the risk remains small. These diseases are not attributed to one risk factor alone, and are usually a combination of several risk factors such as diabetes, increased age, high cholesterol and smoking. Therefore, the risk in a young, otherwise healthy woman is still going to be at the lower end of the scale.
• Women whose pre-eclampsia occurred at an earlier stage in pregnancy or on subsequent rather than first babies are more likely to have an underlying medical predisposition to this type of condition (e.g. underlying lipid disorders or problems with breakdown of sugars). This has led to the suggestion that the association between cardiovascular diseases in later life and pre-eclampsia is caused by the conditions having a common predisposition in the individual.
• This review has combined results from several studies and, although it has done so using reliable statistical methods, the quality of the studies included, types of women followed, and the methods of analysing outcomes in the individual studies are likely to be different. For example, the authors acknowledge that, in older studies, pregnancy-induced hypertension may have been misclassified as pre-eclampsia. It is also not possible to ensure that all possible confounding risk factors in the women have been considered. The researchers considered whether some of these factors might be affecting results, using statistical analyses in some cases, and their investigations suggested that results should not have been affected greatly by these factors.
• The individual studies were mostly carried out in North America, Canada and western Europe, therefore findings may not be applicable to populations with different ethnic backgrounds.

Overall, women who suffered from pre-eclampsia during pregnancy should have their individual cardiovascular risk profile carefully considered by a doctor and commence appropriate treatment if necessary.

Sir Muir Gray adds...

The higher your blood pressure, the greater the risk of heart disease, but if other risks are reduced, for example by doing more walking, the risk of high blood pressure is balanced.