New Approach Improves Identification of Women at High Risk of Preeclampsia

A new meta-analysis examining 92 cohort studies involving over 25 million pregnancies has provided an unprecedented understanding of risk factors for preeclampsia—some risk factors being strong enough to warrant that a pregnant woman starts on prophylactic treatment with acetylsalicylic acid (ASA) when she has only one.

Researchers led by Dr. Joel Ray of St. Michael’s Hospital (Toronto, Ontario, Canada) have developed a new tool that can improve how clinicians identify women at high risk of developing preeclampsia, and who should take ASA (i.e., aspirin). Clinical practice guidelines recommend that women at high risk take ASA daily at low-dose (“baby aspirin”) starting at 12–20 weeks of pregnancy.

The new meta-analysis identified several risk factors that alone, or in combination, provide a clear, concise, evidence-based approach to identifying these women based on routinely collected clinical information. Also importantly, even though ASA is safe in pregnancy, the tool helps distinguish women who are unlikely to benefit from ASA therapy.

Preeclampsia affects approximately 3% of women, and is characterized by onset of elevated blood pressure in later pregnancy. It can cause a woman to seize or have a stroke or kidney failure, and can put fetuses at risk of premature birth and poor growth.

The new study started with the idea that a woman at a 7%–10% or higher chance of developing preeclampsia is a candidate for preventive therapy with ASA. The researchers examined large cohort studies (over 1,000 women each) and pooled the results to determine which individual risk factors pass that threshold.

Some risk factors identified are strong enough that a woman should likely be started on ASA when she has only one factor. These include having had preeclampsia in a previous pregnancy, or diabetes or chronic hypertension prior to the current pregnancy. For example, having chronic hypertension alone produces an absolute risk of 16% of developing preelampsia, compared to a risk of 3% in the absence of chronic hypertension or other risk factors.

However, some risk factors are not strong enough on their own, so a woman would need to have 2 or3 to warrant ASA treatment. For example, a woman who has chronic kidney disease has about a 6% of developing preeclampsia, probably not high enough alone. Among the list requiring 2 or more risk factors are a prior stillbirth or separation of the placenta from the uterus wall, or in the current pregnancy: recognized chronic kidney disease, twins or triplets, lupus, first-time pregnancy, or age > 40 years.

"We can now identify the most influential clinical factors for preeclampsia, none of which require special testing, and all are currently collected by a midwife, obstetrician, family doctor, or nurse practitioner at a woman's routine pregnancy visit," said Dr. Ray, "While ASA may reduce the risk of pre-eclampsia, we really want to ensure that only a woman truly at high risk goes on ASA, while making it very easy for any clinician to identify that person."

The study was published April 19, 2016, in the journal BMJ.

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