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WASHINGTON -- Consensus is growing that clinicians can be confident treating mild hypertension in otherwise healthy pregnant women without hurting their babies, based on the CHAP study.

In this large randomized trial, treating high blood pressure (BP) to a target of <140/90 mm Hg resulted in better outcomes than did usual care, as evidenced by the reduced combined incidence of pre-eclampsia with severe features, medically indicated preterm birth at less than 35 weeks' gestation, placental abruption, and fetal or neonatal death (30.2% vs 37.0%, adjusted RR 0.82, 95% CI 0.74-0.92), reported Alan Tita, MD, PhD, of the University of Alabama at Birmingham.

Notably, hypertension treatment did not appear to harm babies or mothers. The study's treatment and control groups did not differ in the safety outcomes of small-for-gestational-age births below the 10th percentile, serious maternal complications, or severe neonatal complications, he said in a presentation at the American College of Cardiology (ACC) meeting. The results were simultaneously published in the (NEJM).

CHAP persevered through difficult recruitment to enroll over 2,400 pregnant women.

This trial is "practice-changing," as "one of the reasons we don't have as much data in pregnant patients is some of the logistical and ethical concerns that we've had," according to ACC immediate past president Athena Poppas, MD, of Warren Alpert Medical School of Brown University in Providence, Rhode Island, during the session's panel discussion.

Indeed, Tita noted that major pregnancy and obstetrics societies are already aware of CHAP and working to incorporate the results in new recommendations. "In the next few weeks, we'll see some momentum to move toward these new findings," he said at an ACC press conference.

Chronic high BP has previously been tied to pre-eclampsia, preterm birth, maternal death, heart failure, and stroke in pregnant women.

For the CHAP study, Tita's group enrolled 2,408 pregnant women with mild chronic hypertension and singleton fetuses at a gestational age of less than 23 weeks. Notably, this was a relatively diverse cohort, with nearly half of people being Black.

Participants were randomized to receive antihypertensive medications or have treatment withheld until the development of severe hypertension (>160/105 mm Hg). The preferred antihypertensives were labetalol and extended-release nifedipine.

Between the groups, there was a small difference in mean BP from randomization to delivery: 129.5/79.1 mm Hg with treatment versus 132.6/81.5 mm Hg for controls.

Tita acknowledged that his group is not sure whether one of the two study drugs was better for patients based on the trial.

"Studies of the long-term effect of antihypertensive treatment on cardiovascular and other outcomes in pregnant women with mild chronic hypertension and their offspring may further clarify the role of antihypertensive therapy," the authors added.

"The virtually identical values for placental weight in the two treatment groups [466.3 g vs 464.6 g, treatment effect 1.67, 95% CI -17.57 to 20.91] give further assurance of the safety of the active treatment. The absence of any evidence of reduced fetal growth with more aggressive treatment is very reassuring and is consistent with the findings of the investigators," said NEJM editors Michael Greene, MD, and Winfred Williams, MD, both of Massachusetts General Hospital in Boston.

They highlighted the apparent reduction of pre-eclampsia-related outcomes after hypertension treatment in an .

"As secondary outcomes not adjusted for multiplicity, these findings must be regarded with caution. However, if the results are confirmed in subsequent studies, such outcomes would be a compelling reason to change the recommendations for clinical practice regarding the treatment of mild hypertension during pregnancy," Greene and Williams wrote.