Study Shows Treating Pre-Existing High Blood Pressure in Pregnancy Improves Maternal and Fetal Outcomes

More than 2 percent of pregnant women in the United States have chronic hypertension, or high blood pressure. Medical professionals agree that severe chronic hypertension during pregnancy should be treated with medications. Treating non-severe or mild forms of chronic hypertension during pregnancy, however, has led to a divide in medical recommendations for decades.

A new study published recently in the New England Journal of Medicine provides evidence that treating mild chronic hypertension with medications is beneficial and safe for the mom and baby. The findings provide for the first time comprehensive, evidence-based data for treating non-severe forms of chronic hypertension during pregnancy.

The results are from the Chronic Hypertension and Pregnancy trial, or CHAP, consortium of more than 60 clinical sites across the United States, including Oklahoma Children’s Hospital OU Health, led by the University of Alabama at Birmingham. The trial evaluated the effects of prescribing blood pressure medication to pregnant women with mild chronic hypertension. The study results showed this treatment improved pregnancy outcomes without compromising the baby’s growth and overall health, which has been a primary concern from physicians for years.

Chronic hypertension increases the risk for pregnancy complications, including maternal and perinatal death. The condition is associated with a three- to five-times increased risk for preeclampsia, placental abruption, preterm birth, small for gestational age newborns and perinatal death. It is also associated with a five- to 10-times increased risk for maternal death, heart failure, stroke, pulmonary edema and acute kidney injury.

“The results of this study close a significant gap in knowledge, and dissemination of this information will result in improved maternal, fetal and neonatal outcomes,” said Rodney K Edwards, M.D., co-author of the publication and OU Health site principal investigator for the CHAP trial. Edwards is also Presbyterian Health Foundation Endowed Chair of Perinatal Research and Professor and Chief, Section of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, at the University of Oklahoma Health Sciences Center College of Medicine.

The CHAP consortium launched the CHAP program in 2014 with funding from the National Institutes of Health’s Heart, Lung and Blood Institute. From September 2015 to March 2021, CHAP enrolled more than 2,400 pregnant women with known mild chronic hypertension, whose blood pressure was between than 140/90 and 160/105.

Notably, the CHAP trial is one of the most comprehensive and diverse studies of its kind. The Black patient population is disproportionately affected by chronic hypertension, and almost 50 percent of study participants were Black mothers.

Participants were randomized into active and standard treatment groups. The active group was prescribed blood pressure medication. The standard group received medication only if a participant developed more severe hypertension, or blood pressure greater than 160/105 mmHg. Participants were evaluated in routine clinic visits through six weeks after delivery.

There was an almost 20 percent decrease in pregnancy complications for women treated with medication compared to the standard group. Complications included severe preeclampsia and preterm births before 35 weeks’ gestation.

Preterm births before 35 weeks’ gestation were also significantly reduced in the active group, from more than 16 to 12 percent. Babies born before 35 weeks have an increased chance for short-term morbidities, long-term health complications, and intellectual and developmental disabilities.

Additionally, the active group saw reductions in frequency of severe maternal hypertension, any preeclampsia with or without severe features, and any preterm birth before 37 weeks. There was slight or no difference in maternal cardiovascular complications and neonatal complications between the two study groups. Importantly, newborn size was also not affected by treatment.