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There was a steady increase in the prevalence of chronic hypertension in pregnancy over the last two decades, with some accompanying changes in treatment, a nationwide cohort study found.

From 2008 to 2021, the prevalence of chronic hypertension in pregnancy increased from 1.8% to 3.7%, matching trends reported for other adult populations, according to researchers led by Stephanie Leonard, PhD, of Stanford School of Medicine in California, reporting in .

The use of blood pressure (BP)-lowering medications in pregnant women remained stable at around 57-60% during this period -- contrary to expectations since guidelines from the American College of Cardiology (ACC) and American Heart Association (AHA) had been updated in 2017.

"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," said Leonard .

What did change from 2008 to 2021, her group found, was the sharp decrease in the use of methyldopa (from 29% to 2%) among pregnant women with chronic hypertension. This is in line with the American College of Obstetricians and Gynecologists (ACOG) removing methyldopa from its recommendations in 2019 after a Cochrane Review found beta-blockers and calcium-channel blockers to be more effective than this agent in reducing the risk of severe hypertension in pregnancy.

Indeed, Leonard's group reported increased use of labetalol (from 19% to 42%) and nifedipine (from 9% to 17%). Additionally, hydrochlorothiazide fell somewhat out of favor (11% to 5%) during the study period.

Distinct from new-onset hypertensive complications of pregnancy such as preeclampsia and gestational hypertension, chronic hypertension in pregnancy is defined by ACOG as BP ≥140 mm Hg systolic and/or 90 mm Hg diastolic before pregnancy or before 20 weeks of gestation, use of antihypertensive medications before pregnancy, or persistence of hypertension for over 12 weeks after delivery.

Chronic high BP is known to have associations with preeclampsia, preterm birth, maternal death, heart failure, and stroke in pregnant women.

The unchanged use of antihypertensives in pregnancy in the present study may be related to ACOG, unlike the ACC/AHA, having held back on endorsing these medications until more recently.

"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," commented 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, in an .

This fear of treating chronic hypertension during pregnancy had been challenged by 2022's CHAP trial, in which treating BP to a target of <140/90 mm Hg resulted in a lower incidence of adverse events compared with having antihypertensives withheld until women met criteria for severe hypertension.

As a result, ACOG started recommending antihypertensive treatment of such mild hypertension in pregnancy in 2022.

"Of course, the impact of the CHAP trial and ACOG's revised practice recommendations is beyond the scope of Leonard's study, but further analysis is likely to show increases in antihypertensive medication after 2022, corresponding with aligning recommendations between ACOG and ACC/AHA," according to Brandt and Ananth.

Study authors utilized the Merative Marketscan Research Database and found records of over 1.9 million pregnancies based on American commercial insurance claims from 2007 to 2021.

Leonard's team acknowledged that they used data on medications dispensed as a proxy for actual use. Moreover, they lacked the BP measurements needed to assess severity of hypertension, and could not generalize findings to people without commercial health insurance.

Without the data to explain why they saw an increase in the prevalence of chronic hypertension in their report, Leonard and colleagues cited similar findings from prior work suggesting that the increasing trend in chronic hypertension during pregnancy is attributable in part to increasing maternal age, with increased vigilance in diagnosis and coding perhaps also playing a role.

"This study highlights the growing burden of chronic hypertension and poor cardiovascular health pre-pregnancy as critical targets to improve maternal health," said Sadiya Khan, MD, MSc, of Northwestern Medicine in Chicago, in the press release.

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