CHAP: Treating Mild Chronic HTN is Associated With Better Pregnancy Outcomes

Treating mild chronic hypertension during pregnancy was associated with better pregnancy outcomes than a strategy of reserving treatment only for severe hypertension, based on findings from the CHAP trial presented April 2 at ACC.22 and simultaneously published in the New England Journal of Medicine (NEJM). Researchers also observed no increase in the risk of infants born with "small-for-gestational-age birth weight."

The open-labeled, randomized, controlled trial enrolled 2,408 women with known mild chronic hypertension (<160/110 mm Hg) and who were less than 23 weeks into their pregnancy at 61 sites between 2015 and 2021. Women were similar across groups with over half (56%) already on medication for hypertension at enrollment; 48% were Black, 28% non-Hispanic White and 20% Hispanic.

A total of 1,208 pregnant women were assigned to receive treatment with a first-line antihypertensive medication with a blood pressure goal of less than 140/90 mm Hg, and another 1,200 received no treatment unless blood pressure became more severe (160/105 mm Hg or higher). Centers were given general guidance on which medications to prescribe – mainly labetalol or nifedipine, which were provided by the study – using the patient's previously prescribed dose or the lowest recommended dose and escalating the dose during clinic visits to achieve the blood pressure goal. Women in the treatment group who were already taking other blood pressure-lowering medication could remain on that drug if they wished and as long as it was safe in pregnancy.

Researchers found significantly lower rates of the primary outcome – a composite of preeclampsia with severe features, preterm birth less than 35 weeks, abruption and neonatal/fetal death – among pregnant women who received treatment (30.2%) compared with those who did not (37%). When looking at each outcome individually, antihypertensive treatment significantly lowered the risk for preeclampsia and birth before 35 weeks. The rates of placenta abruption and fetal or neonatal death were not significantly different between the groups. Researchers did not see a significant difference in the rate of babies who were small for gestational age – the study's safety endpoint – between the two groups, with 11.2% of babies in the treatment group and 10.4% of babies in the no treatment group falling below the 10th percentile.

In terms of secondary outcomes, fewer women in the treatment group experienced any preeclampsia or preterm birth compared with women in the no treatment group (24.4% vs. 31% and 27.5% vs. 31.4%, respectively). Maternal death was similar and rare overall. In general, maternal cardiovascular outcomes appeared more favorable, although not significantly better, among women whose hypertension was treated, especially for maternal death, pulmonary edema, kidney failure and ICU admissions. The same was true for severe neonatal complications, researchers said.

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," said Alan Tita, MD, PhD, the study's lead author. "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."

In a related editorial published in NEJM, Michael F. Greene, MD, and Winfred W. Williams, MD, explain, "The most exciting finding in this trial (possibly the result of the large enrollment) is the apparent reduction in the incidence of various measures of preeclampsia in the active-treatment group, findings that have not been observed in eight previous randomized trials … 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."

Clinical Topics: Diabetes and Cardiometabolic Disease, Prevention, Vascular Medicine, Hypertension

Keywords: ACC Annual Scientific Session, ACC22, Pregnancy, Antihypertensive Agents, Pregnancy Outcome, Hypertension, Hypertension, Pregnancy-Induced, Pregnancy Complications, Cardiovascular

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