Thresholds for diagnosing hypertension in pregnancy should not be lowered

King’s College London

New study shows that lowering the threshold for a high blood pressure diagnosis in pregnant women is unlikely to lead to improved outcomes in low-resource settings.

Mother carrying baby

In 2017, the American College of Cardiologists (ACC) and the American Heart Association (AHA) proposed that doctors and nurses should use lower blood pressure levels to diagnose high blood pressure (hypertension). However, what remained unclear was whether these lower numbers should be used to guide the care of pregnant women.

Investigators from King’s College London and institutes in Pakistan, Mozambique, India and Canada have studied the associations between blood pressure thresholds during pregnancy and adverse outcomes for just over 21 000 women and their babies in low-resource settings. Over 100 000 standardised blood pressure measurements, taken in women’s homes, were included in the study.

The research, recently published in Lancet Global Health, found that only women with stage 2 hypertension – non-severe (140-159/90-109mmHg) or severe (greater than or equal to 160/110mmHg) ­– as discrete diagnostic categories, experienced more adverse outcomes than women with normal blood pressure. However, severe stage 2 hypertension was the only blood pressure threshold that reliably identified women at increased risk for maternal central nervous system events (like stroke) or baby death, particularly stillbirth.

Joint lead author and King’s Professor, Laura A. Magee, states:

Through this collaboration with the participating women, their families, their communities, and our academic partners in Pakistan, Mozambique, and India, we have determined that current guidelines for diagnosing hypertension in pregnancy should not change. What remains particularly important is to recognise the particular risks associated with very high blood pressure in pregnancy, especially those of seizures and strokes for mothers, and stillbirth for their babies.”– Professor Laura A. Magee

Lowering the threshold of a high blood pressure diagnosis would substantially increase the burden on health systems already under stress, and could be justified only by the ability to identify women and babies at risk.

While severe hypertension and pre-eclampsia pose serious risks to pregnant women and their babies, women classified as having elevated blood pressure or stage 1 hypertension did not have an increased risk of adverse maternal, fetal, or neonatal outcomes compared to women with normal blood pressure.

As a result, the ACC and AHA’s recommendation to use lower blood pressure values to identify high blood pressure in pregnancy would not improve health workers’ ability to anticipate adverse outcomes in pregnant women.

Taking women’s blood pressure is regarded to be a core element of antenatal and postnatal care. This study confirms the importance of those measurements, as a part of an integrated approach to pregnancy care as the global health community aims to reduce adverse pregnancy outcomes wherever women live.”– Professor Laura A. Magee

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