Study Highlights Benefits of Treating Mild Chronic Hypertension During Pregnancy

Chronic hypertension is a complication that affects up to 6% of pregnant people in the United States. The American College of Obstetricians and Gynecologists (ACOG) describes it as high blood pressure that develops before pregnancy or during the first half of pregnancy. If someone was taking blood pressure medication before they got pregnant—even if their blood pressure is currently normal—they are considered to have chronic hypertension.

Treatment for chronic hypertension during pregnancy depends on whether your high blood pressure is mild or severe, according to ACOG. Blood pressure typically goes down in the first half of pregnancy, and if hypertension is mild, it may stay at that level, or return to normal. In this case, your OB/GYN may decrease your blood pressure medication, or advise you to stop taking it altogether for the remainder of your pregnancy. 

But if your hypertension is more severe, or is causing additional health issues, you may need to start taking—or continue—blood pressure meds during pregnancy.

In a recent study of more than 2,400 pregnant women, researchers found that those who were treated with medication for high blood pressure present before or during the first 20 weeks of pregnancy experienced fewer adverse pregnancy outcomes compared to adults who did not receive antihypertensive treatment. 

A Closer Look at the Study

The study, which was published in the New England Journal of Medicine and presented at the American College of Cardiology’s 71st Annual Scientific Session and Expo on April 2, provides evidence that treating mild chronic hypertension is beneficial and safe for the mom and baby. 

Guidelines for the general non-pregnant population recommend treating chronic hypertension. However, before this research, it was unclear and controversial whether to treat pregnant people with non-severe high blood pressure, says Alan Tita, MD, PhD, professor of obstetrics and gynecology in the UAB Marnix E. Heersink School of Medicine and lead author of the paper.

Hypertension during pregnancy can be treated with blood pressure meds, but not all are considered safe for pregnant people. Angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers, and renin inhibitors are generally avoided during pregnancy.

Dr. Tita and his team found that people who received medication to lower their blood pressure below 140/90 mm Hg during early pregnancy were less likely to have a preterm birth or experience one of several severe pregnancy complications. The treatment did not impair fetal growth.  

The participants were randomized into two treatment groups. The active group received blood pressure medication to keep blood pressure below 140/90 mmHg. The standard group received medication only if a participant developed more severe hypertension (blood pressure greater than 160/105 mmHg). Evaluation during routine clinic visits through six weeks after delivery showed an almost 20 percent decrease in pregnancy complications for women treated with medication compared to the standard group. 

Complications of Chronic Hypertension During Pregnancy

If you are diagnosed with chronic hypertension during pregnancy, you may be at greater risk for preeclampsia and preterm birth (before 35 weeks’ gestation).

Mild preeclampsia, which is characterized by a new onset of a blood pressure greater than 140/90 and urine proteinuria greater or equal to 300 mg/24 hours, can be monitored closely and the patient can be on home bed-rest with frequent visits to the obstetrician until the baby is mature, says Sherry Ross, MD, OB/GYN and women’s health expert at Providence Saint John’s Health Center in Santa Monica, California.

However, severe preeclampsia—when blood pressures are greater than 160/110 and urine proteinuria is 3+ or greater on a urine dipstick—can cause maternal seizures, placenta abruption, and even fetal and maternal death, warns Dr. Ross. This makes early diagnosis and intervention crucial. 

"Between 70 and 80% of pregnant women with chronic hypertension fall into the ‘mild’ category where there is not a medical consensus for treatment," says Dr. Tita. “In light of these new data, it is important that we reevaluate current recommendations, update practice guidelines and begin treating most—if not all—pregnant women with chronic hypertension with medication.”