Treating Mild Chronic Hypertension Improves Pregnancy Outcomes

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Chronic hypertension occurs in at least 2% of pregnancies in the United States and is associated with high rates of preeclampsia and other adverse pregnancy outcomes. There is ongoing debate over treatment strategies: Continuing antihypertensive therapy during pregnancy reduces the risk of severe hypertension but has not previously been shown to improve maternal, fetal, or neonatal outcomes.

Findings from a new trial reported in The New England Journal of Medicine suggest that pregnancy outcomes are improved by antihypertensive therapy for women with mild chronic hypertension, with a blood pressure target of less than 140/90 mm Hg.

The Chronic Hypertension and Pregnancy (CHAP) trial included 2402 pregnant women with mild chronic hypertension, defined as blood pressure of less than 140/90 mm Hg, enrolled from more than 70 US centers. The researchers found treatment for mild chronic hypertension was associated with a reduced risk of adverse pregnancy outcomes.

Women eligible for the trial had singleton fetuses at gestational age less than 23 weeks. In open-label fashion, they were randomly assigned to active treatment, consisting of antihypertensive medications recommended for use in pregnancy, or no treatment unless severe hypertension developed, which was defined as systolic blood pressure of 160 mm Hg or higher or diastolic blood pressure of 105 mm Hg or higher.

Pregnancy outcomes were compared between groups, including a composite primary outcome of preeclampsia with severe features, medically indicated preterm birth at less than 35 weeks’ gestation, placental abruption, or fetal or neonatal death. Additionally, small-for-gestational-age birth weight under the 10th percentile for gestational age was evaluated as a safety outcome.

The primary outcome rate for those treated for mild chronic hypertension was 30.2% compared with 37.0% for the control group, with an adjusted risk ratio (RR) of 0.82. There was no significant difference in the rate of small-for-gestational age birth weight: 11.2% and 10.4%. Likewise, serious maternal complications were similar between the groups: 2.0% with treatment for mild chronic hypertension and 2.6% with the deferred strategy. The incidence of severe neonatal complications was 2.0% versus 2.6%.

The mild hypertension strategy was associated with a lower incidence of any preeclampsia: 24.4% versus 31.1%, RR 0.79. The study intervention was also associated with a lower incidence of preterm birth: 27.5% versus 31.4%, RR 0.87.

The CHAP results suggest that antihypertensive therapy for pregnant women with mild chronic hypertension, with a blood pressure target of less than 140/90 mm Hg, reduces the risk of adverse pregnancy outcomes including preeclampsia, without increasing the risk of small-for-gestational age birth weight. The researchers noted: “[W]e found that active treatment with antihypertensive drugs improved pregnancy outcomes without apparent harm” [Tita AT, et al. Treatment for mild chronic hypertension during pregnancy. N Engl J Med, published online ahead of print April 2, 2022; doi: 10.1056/NEJMoa2201295;].