Researchers Propose Lowering Blood Pressure Guidelines During Pregnancy

Lowering the threshold for high blood pressure in pregnancy may help identify more women who are at risk of life-threatening complications, according to new research.

The March study, which was published in JAMA Open Network, explored new parameters of hypertension, or high blood pressure, a metric that is currently confusing for pregnant women.

In 2017, the American College of Cardiology and the American Heart Association changed the definition of hypertension, lowering the threshold from 140/90 mm Hg and above to 130/80 mm Hg and above, lead study author Natalie A. Bello, MD, MPH, director of research at the Women’s Heart Center at Columbia University Medical Center in New York, tells Verywell.

But, despite these lowered metrics, the American College of Obstetrics and Gynecology did not change the threshold for diagnosing hypertension during pregnancy. That threshold is still at 140/90 mm Hg and higher.

For the study, Bello and her colleagues analyzed data of 137,389 pregnancies from 2009 to 2014 to look for hypertension and pregnancy outcomes. When they applied the lowered definition of hypertension from the American College of Cardiology and the American Heart Association, they discovered that the prevalence of hypertension in pregnant women jumped from 10.3% to 28.1%.

Lowering the Threshold

Women who met the criteria for hypertension under the lowered threshold also had a larger risk of preeclampsia, a potentially dangerous pregnancy complication that can cause organ damage. The researchers discovered that women in this group had a nearly five times greater risk of hypertension compared to those who didn’t have hypertension by either definition. 

“The discrepant definitions/thresholds for the diagnosis of hypertension between pregnant and non-pregnant adults can be a source of confusion for patients and clinicians,” Bello says. “We knew that lowering the threshold would increase the prevalence of hypertension, but were unsure how much it would increase, and whether applying that diagnosis would better identify women and their fetuses who are at risk of adverse events such as preeclampsia, or if it would not make a difference.”

Ultimately, Bellow says, using the lowered criteria to diagnose hypertension in pregnant women led to a nearly 21% improvement in identifying women at risk of developing preeclampsia, and a nearly 4% improvement in finding babies at risk for related health issues like small birth weight, preterm birth, and being admitted to the NICU.

Hypertension in Pregnancy

Hypertension in pregnancy is generally divided into three categories:

• Gestational hypertension. This is high blood pressure that develops after 20 weeks of pregnancy. Women with gestational hypertension often don’t have any symptoms, and the condition goes away within 12 weeks after childbirth. It can increase the risk of having high blood pressure in the future, along with low birth weight or preterm birth.
• Chronic hypertension. This is high blood pressure that starts before 20 weeks of pregnancy or before a woman became pregnant.
• Preeclampsia. This condition is a sudden increase in blood pressure after 20 weeks of pregnancy, and it usually happens in the last trimester. The condition may be detected by signs of damage to some organs, like the liver or kidneys. Preeclampsia can be serious or life-threatening for an expectant mother and her baby.

The exact cause of preeclampsia is unknown, but women are more at risk when they have certain health factors, including:

• Having high blood pressure or chronic kidney disease before pregnancy
• Having high blood pressure or preeclampsia in a previous pregnancy
• Having obesity
• Being over age 40
• Being pregnant with more than one baby
• Being African American
• Having a family history of preeclampsia
• Having certain health conditions, such as diabetes or lupus 
• Having used in vitro fertilization, egg donation, or donor insemination

“High blood pressure during pregnancy can be dangerous for both the mother and the developing baby, and oftentimes requires monitoring,” women’s health expert Jennifer Wider, MD, tells Verywell.

 ‘Baby Aspirin’ May Help

Currently, the United States Preventive Services Task Force (USPSTF) recommends that pregnant women have their blood pressure checked at every prenatal care visit. “If the reading is elevated, it should be confirmed with repeated measurements,” Bello says.

Cases of high blood pressure in pregnant women are often treated with a low-dose “baby aspirin,” Bello says. Research has also found that low-dose aspirin—between 81 to 160 milligrams—could help prevent preeclampsia in women who are in the first stage of high blood pressure.

Bellow urges pregnant women with high blood pressure or borderline high blood pressure to talk to their care providers about whether they could benefit from taking a baby aspirin to prevent preeclampsia.