The number of pregnant women with chronic high blood pressure doubled during the past decade and a half, but treatment remains low among them, a new study found.

About 3.7% of pregnant women were diagnosed with high blood pressure in 2021, up from 1.8% in 2008, researchers said.

However, prescriptions handed out to pregnant women for high blood pressure remained about the same, with only 60% getting drugs that could lower their blood pressure.

“While the rate of hypertension in pregnancy has doubled, the use of medication for treatment remained stable at only 60%, which we believe is likely below what it should be if patients are treated according to clinical guidelines,” said lead researcher Stephanie Leonard, an epidemiologist with Stanford University School of Medicine.

For the study, published June 17 in the journal Hypertension, researchers analyzed a database of private health insurance claims for 2007 to 2021, reviewing records for 1.9 million pregnancies during that period.

They found that the frequency of high blood pressure diagnosis during pregnancy continued to rise steadily over the past decade and a half.

However, the researchers were surprised to find no spike in diagnoses following a 2017 guideline update that lowered the threshold for early-stage high blood pressure.

“We had hoped to see some impact from the 2017 guideline, which reduced the blood pressure threshold for treatment of hypertension,” Leonard said in a journal news release. “We were surprised to not find any meaningful changes from before and after the guideline.”

Pregnant women with high blood pressure tended to be 35 or older, living in the South and suffering from other chronic health conditions like obesity, diabetes or kidney disease.

Chronic high blood pressure during pregnancy can cause liver or kidney damage, and can double a woman’s risk of future heart failure and other heart disease, the researchers noted.

“Since nearly 1 in 3 individuals with chronic hypertension may face a pregnancy complication, the prevention and control of hypertension should be among the highest priorities for improving maternal health,” said Dr. Sadiya Khan, a professor of cardiovascular epidemiology at Northwestern University who was not involved in the study.