Active Treatment for Mild Hypertension in Pregnancy Safe for Mother and Child, Study Finds

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Results of the CHAP project demonstrate active treatment of chronic mild hypertension was associated with reductions in risk of adverse pregnancy outcomes and is unlikely to harm the developing child.

The debate surrounding the best treatment approach management of hypertension in pregnant women seems to have an answer, with results of the CHAP project detailing the effects of antihypertensive treatment on risk of adverse pregnancy outcomes in pregnant women with mild hypertension.

An open-label, randomized, controlled trial of more than 2000 pregnant women with mild chronic hypertension, results of the study, which were presented during the American College of Cardiology’s 71st Annual Scientific Sessions, demonstrate a strategy ion targeting a blood pressure below 140/90 mmHg was associated with more favorable pregnancy outcomes, without increasing risk of small-for-gestational-age birth weight, than a strategy of only treating severe hypertension.

“We have known for a long time that—outside of pregnancy—it’s important to treat high blood pressure to improve outcomes, including reducing cardiovascular events and death, but there has been some controversy and uncertainty whether to treat non-severe chronic hypertension during pregnancy, mostly due to concerns that antihypertensive treatment could lead to poor fetal growth,” said Alan Tita, MD, PhD, director of the Center for Women’s Reproductive Health, professor of obstetrics and gynecology at University of Alabama Heersink School of Medicine and the study’s lead author. “Our trial addresses the benefits and safety of treating non-severe chronic hypertension during pregnancy.”

While the effects of blood pressure control on risk of cardiovascular events thoroughly demonstrated in previous studies, there is no consensus on an evidence-based approach to mild chronic hypertension in pregnant women. Launched by investigators at the University of Alabama at Birmingham in September 2015, the Chronic Hypertension and Pregnancy (CHAP) project was an investigator-initiated trial conducted in 70 sites across the US, including major institutions such as Columbia University, Washington University School of Medicine, Duke University, and the University of Texas Southwestern Medical Center.

The primary efficacy outcome of interest was a composite of preeclampsia with severe features, preterm birth prior to 35 weeks’ gestation, abruption, and neonatal/fetal death. The study’s primary safety outcome was small-for-gestational age births. Secondary outcomes of interest for the study included preterm birth prior to 37 weeks’ gestation and preeclampsia.

From September 2015 through March 2021, a total of 29,772 women underwent screening and 2419 underwent randomization. Investigators noted 10 patients were immediately withdrawn after randomized and an additional patient withdrew consent. Ultimately, 1208 were randomized to active treatment and 1200 were randomized to the control arm, with baseline characteristics well-balanced between the 2 arms.

Among the entire study cohort, 56% had known chronic hypertension and were receiving medication, 22% had known chronic hypertension and were not receiving medication, and 22% had newly diagnosed chronic hypertension. Among those in the active treatment group, 61.7% received labetalol, 35.6% received nifedipine, and 2.7% received other medications. At 86% of study visits, patients in the active treatment group reported taking their assigned medications.

Upon analysis, results indicate the incidence of a primary outcome event was lower among those in the active treatment group compared to those in the control arm, with events occurring in 30.2% and 30.7%, respectively (aRR, 0.82 [95% CI, 0.74-0.92]; P <.0001). When assessing small-for-gestational-age births, results suggested the percentage among those in the active treatment group was 11.2% compared with 10.4% in the control group (aRR, 1.04 [95% CI, 0.82-1.31]; P=.76).

Safety analyses indicated the incidence of serious maternal complications was 2.1% and 2.8% among those in the active treatment arm and the control arm, respectively (RR, 0.75 [95% CI, 0.45-1.26]), and the incidence of severe neonatal complications was 2.0% and 2.6%, respectively. (RR, 0.77 [95% CI, 0.45-1.30]). Additionally, results suggested the incidence of any preeclampsia in the study arms was 24.4% in the treatment arm and 31.1% in the control arm, respectively (RR, 0.79 [95% CI, 0.69-0.89]), and the incidence of preterm birth were 27.5% and 31.4%, respectively (RR, 0.87 [95% CI, 0.77-0.99]).

“After many decades of uncertainty, results of this study support the need for clinical guidance to treat mild as well as severe chronic hypertension in pregnancy and to educate patients about the benefits of doing so,” Tita added. “To date, there have been disparate recommendations and hesitancy to treat women with milder forms of high blood pressure during pregnancy for fear of hurting the growing fetus but based on the data, doing so may be good for mom and baby.”

This study, “Treatment for Mild Chronic Hypertension during Pregnancy,” was presented at ACC.22 and simultaneously published in the New England Journal of Medicine.