Abstract
Mild chronic hypertension affects up to 80% of pregnant women with hypertension and is associated with increased risks of preeclampsia, preterm birth, placental abruption, and maternal morbidity. Historically, clinicians avoided treating mild hypertension due to concerns about fetal growth restriction. The CHAP Trial, a large multicenter randomized study of 2,408 pregnant women, tested whether targeting blood pressure below 140/90 mm Hg improves outcomes. Women receiving antihypertensive therapy experienced significantly fewer adverse pregnancy outcomes without increased risk of small‑for‑gestational‑age infants. These findings provide definitive evidence supporting treatment of mild chronic hypertension during pregnancy and have reshaped national guidelines.
Impact Story
Chronic hypertension affects more than 2% of pregnancies in the United States and disproportionately impacts Black women, contributing to persistent maternal health inequities. For decades, clinicians faced a critical dilemma: treat mild chronic hypertension and risk impaired fetal growth, or withhold treatment and risk severe maternal complications. Evidence was inconsistent, and guidelines varied widely.
The CHAP Trial, led by UAB’s Dr. Alan T. Tita and a national consortium of investigators, addressed this question through a rigorous multicenter randomized study involving 2,408 pregnant women. By comparing active antihypertensive treatment to a conservative “treat only if severe” approach, the trial demonstrated that maintaining blood pressure below 140/90 mm Hg significantly reduces preeclampsia, preterm birth, and other serious complications—without increasing the risk of small‑for‑gestational‑age infants.
These findings overturned long‑standing assumptions and provided definitive evidence that early treatment is both safe and beneficial. The results have already influenced national guidelines, including updates from the American College of Obstetricians and Gynecologists (ACOG), and are shaping clinical practice across the country. The CHAP Trial exemplifies how translational research can directly improve maternal health, advance equity, and save lives.
TSBM Benefit
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Clinical and Medical Benefit |
Therapeutic Procedures: The study provided treatment procedures for continuous treatment of pregnant women who already present with mild CHTN as well as those who develop mild CHTN during their pregnancy. Guidelines: A practice advisory issued from the American College of Obstetrics and Gynecology (ACOG) recommends utilizing 140/90 as the threshold for initiation or titration of medical therapy for chronic hypertension in pregnancy, rather than the previously recommended threshold of 160/110. The Society for Maternal and Fetal Medicine is reviewing the study for potential recommendations as well. |
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Community & Public Health Benefits |
Disease Prevention & Reduction: Treatment beginning at 140/90 mm Hg did not increase the risk of low birthweight. Life Expectancy & Quality of Life: Women who were treated at the lower threshold had lower risk of one or more primary-outcome events of preeclampsia with severe features, medically-indicated preterm birth at less than 35 weeks' gestation, placental abruption, or fetal or neonatal death. |
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Economic Benefits |
Societal & Financial Costs of Illness: Lowering maternal risks during pregnancy, and reducing ICU admissions for babies could reduce the substantial economic cost of mild CHTN. |
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Standards & Practice Benefits |
Standards: National board recommendations changed based on the results of this trial. |
