Chronic Hypertension in Pregnancy Increased Two-Fold Between 2008 and 2021

The prevalence of chronic hypertension during pregnancy doubled between 2008 and 2021, increasing from 1.8% to 3.7%, while use of antihypertensive medications in pregnant women remained low, although stable, at 60% during the same period.

The findings, based on a nationwide review of commercial health insurance claims linked to 1.9 million pregnancies, were published in the journal Hypertension.

The steady rise over the 14-year period without a spike in new diagnoses or an increase in antihypertensive prescribing was contrary to what study authors had expected, based on revisions in 2017 to the American Heart Association/American College of Cardiology (AHA/ACC) clinical guideline on hypertension. "We had hoped to see some impact from the 2017 guideline, which reduced the blood pressure threshold for treatment of hypertension. We were surprised to not find any meaningful changes from before and after the guideline," lead study author Stephanie Leonard, PhD, assistant professor (research) of obstetrics and gynecology at the Stanford School of Medicine in California, said in an AHA press release. The steady prescribing rate of 60% “is likely below what it should be if patients are treated according to clinical guidelines,” Leonard added.

There was a change, however, in the use of methyldopa to treat chronic hypertension in women during pregnancy, with the number decreasing from 29% to 2%, according to the study findings. Leonard and colleagues point to removal of the drug from recommendations of the American College of Obstetricians and Gynecologists (ACOG) in 2019, the change based on data showing beta blockers and calcium channel blockers to be more effective in reducing the risk of severe hypertension in the vulnerable population. The use of hydrochlorothiazide also fell during the study period, from 11% to 5%.

In contrast, the researchers found an increase in the proportion of pregnant women treated with labetalol (from 19% to 42%) and nifedipine (from 9% to 17%), both currently recommended as

ACOG defines chronic hypertension in pregnancy as BP ≥140 mm Hg systolic and/or 90 mm Hg diastolic before pregnancy or before 20 weeks of gestation, the use of antihypertensive medications before pregnancy, or persistence of hypertension for more than 12 weeks after delivery. The elevation has well-recognized associations with preeclampsia, preterm birth, maternal death, heart failure, and stroke in pregnant women.

ACOG did not adopt or endorse the revised AHA/ACC guideline for the diagnosis of hypertension and preferred pharmacotherapy when it was first published. "In the face of divergent guidelines, Leonard's results suggest that obstetricians and cardiologists did not substantially change practices around antihypertensive medication utilization in pregnancy. This reflects, perhaps, a long-held belief that treatment of chronic hypertension, especially mild forms, could potentially reduce fetal perfusion and lead to untoward effects on fetal growth and well-being," Justin Brandt, MD, of NYU Langone Health in New York, and Cande Ananth, PhD, MPH, of Rutgers Robert Wood Johnson Medical School in Brunswick, New Jersey, commented in an editorial accompanying the study.

The practice of reserving antihypertensive treatment until a pregnant woman met criteria for severe disease was challenged by findings in 2022 from the CHAP trial. That study, published in The New England Journal of Medicine, demonstrated that treating blood pressure to less than 140/90 mm Hg was associated with a lower incidence of adverse events, including “no increase in risk for small-for-gestational-age birth weight.”3

Based on the findings in a cohort of nearly 2500 pregnant women, ACOG shifted its position to recommending antihypertensive treatment of mild hypertension in pregnancy in 2022.

Brandt and Anath note that CHAP trial impact and the revision of ACOG’s clinical practice guidelines were beyond the scope of the research by Leonard et al. “But further analysis is likely to show increases in antihypertensive medication after 2022, corresponding with aligning recommendations between ACOG and ACC/AHA," they wrote.

The researchers acknowledged the study’s limitations, including reliance on data for medications dispensed as proxy for their use. They also did not have access to BP values that would have allowed assessment of hypertension severity. Moreover, use of the commercial Merative Marketscan Research Database precludes generalizing any findings to populations without such insurance.

Leonard and colleagues speculate on reasons for the observed increase in prevalence of chronic hypertension during pregnancy. In the absence of data, the team cited findings from previous research as consistent with theirs and that suggest the upward trend may be due in part to increasing maternal age as well as to heightened attention to diagnosis and coding.

The study highlights the growing burden of chronic hypertension in pregnancy as well as of poor cardiovascular health prior to pregnancy. “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,” Sadiya Khan, MD, MSc, of Northwestern Medicine in Chicago, said in the press release.