Clinical Trials That Have Changed Obstetric Practice: The Chronic Hypertension and Pregnancy (CHAP) Trial.

We describe the evolution of treatment recommendations for chronic hypertension (CHTN) in pregnancy, the CHTN and pregnancy (CHAP) trial, and its impact on obstetric practice. The US multicenter CHAP trial showed that antihypertensive treatment for mild CHTN in pregnancy [blood pressures (BP)<160/105 mm Hg] to goal<140/90 mm Hg, primarily with labetalol or nifedipine compared with no treatment unless BP were severe reduced the composite risk of superimposed severe preeclampsia, indicated preterm birth <35 weeks, placental abruption, and fetal/neonatal death. As a result of this trial, professional societies in the United States recommended treatment of patients with CHTN in pregnancy to BP goal<140/90 mm Hg.