Study shows treating mild preexisting high blood pressure during pregnancy improves outcomes for parents and babies

ATLANTA – Treating people with medication for severe chronic hypertension (high blood pressure) during pregnancy is standard practice; however, there has been debate on best methods for treating non-severe or mild forms of chronic hypertension during pregnancy. Now a new study published in the New England Journal of Medicine on April 2, 2022, provides evidence that treating mild chronic hypertension with medications is beneficial and safe for pregnant people and their babies.

Currently the largest trial to study chronic hypertension in pregnancy, the Chronic Hypertension and Pregnancy or CHAP study involved a consortium of more than 60 clinical sites across the U.S., including Emory University. The findings of this study were presented at the American College of Cardiology’s 71st Annual Scientific Session and Expo earlier this month.

Iris Krishna

Iris Krishna, MD, MPH, served as principal investigator of the Chronic Hypertension and Pregnancy or CHAP clinical trial site at Emory.

“There was a strong need for evidence-based data to demonstrate maternal and perinatal benefit with treatment of mild chronic hypertension during pregnancy,” says Iris Krishna, MD, MPH, assistant professor, Division of Maternal-Fetal Medicine, Department of Gynecology and Obstetrics at Emory University School of Medicine and director of perinatal quality, Emory Perinatal Center at Emory University Hospital Midtown. “This is a landmark clinical trial and the findings of this study will lead to a paradigm shift in how we care for pregnant people with mild hypertension.” Krishna was principal investigator of the study site at Emory.

More than two percent of pregnant people in the United States have chronic hypertension. Chronic hypertension increases the risk for pregnancy complications, including maternal and perinatal death. It is associated with increased risk for preeclampsia (a condition marked by sudden high blood pressure and early signs of organ dysfunction after 20 weeks gestation), placental abruption (a condition where the placenta separates from the wall of the uterus), preterm birth, small for gestational age newborns and perinatal death. It is also associated with an increased risk for maternal death, heart failure, stroke, pulmonary edema and acute kidney injury.

In the CHAP study, more than 2,400 pregnant people with a known diagnosis of mild chronic hypertension before pregnancy that were less than 23-weeks pregnant with a single fetus were enrolled. The pregnant participants were randomly assigned to one of two groups: an active treatment group receiving antihypertensive medication, mostly labetalol or nifedipine, recommended for use in pregnancy to keep blood pressure below a systolic (top number) of 140 mm Hg and a diastolic (bottom number) of 90 mm Hg; or a control or standard group, which would receive no medication unless they developed severe hypertension. Severe hypertension is defined as blood pressure with a systolic (top number) above 160 mm Hg or diastolic (bottom number) above 105 mm Hg.

Participants were evaluated in routine clinic visits through six weeks after delivery. The study lasted from September 2015 to March 2021. People who developed gestational hypertension, or high blood pressure during pregnancy after 23-weeks’ gestation were not enrolled in this study.

“The findings showed that participants in the active treatment arm had an almost 20% decrease in pregnancy complications, specifically preeclampsia with severe features and preterm birth before 35-weeks’ gestation, when compared to participants in the standard group,” says Krishna. “Additionally, active treatment did not affect the birth weight of infants.”

The incidence of preeclampsia in the active treatment group was 23.3% and 29.1% in the standard group. The incidence of medically indicated preterm birth less than 35 weeks was 12.2 percent in the active treatment group and 16.7% in the standard group. Birth weights below the 10th percentile in growth were 11.2% in the active treatment group and 10.4% in the standard group. Incidences of serious maternal complications and severe neonatal complications were both lower in the active treatment group, as well.

Krishna goes on to say, “The study findings support the medication treatment of pregnant people with mild chronic hypertension with a blood pressure target of less than 140/90 mm Hg. This treatment will be a best practice to improve maternal and fetal outcomes. Additionally with these findings, pregnant people can continue their established antihypertensive therapy.”

Also of importance, besides its thoroughness, the researchers noted the CHAP study is one of the most diverse studies of its kind.

“The CHAP trial is one of the most comprehensive trials to address this topic and unique to this trial, is its diverse population that closely mirrors pregnant people with mild chronic hypertension in the U.S.,” says Krishna. “Black women are disproportionately affected by chronic hypertension and almost 50% of study participants were Black mothers.”

The CHAP study was funded by the National Heart, Lung, and Blood Institute (NHLBI), part of National Institutes of Health (grant number: 1U01HL119242-01). The University of Alabama at Birmingham served as the consortium’s lead site.

Martina Badell, MD, associate professor in the Division of Division of Maternal-Fetal Medicine, Department of Gynecology and Obstetrics at Emory was a co-investigator on the Emory study.

“I am incredibly grateful for our CHAP study participants, many of whom were eager to participate in this research,” says Krishna. “I am excited to see them for their next pregnancies and tell them we now know best practices for treating mild chronic high blood pressure in pregnancy.”

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