Pregnant woman at doctor's office having pressure measured.

Chronic hypertension in pregnancy: To treat or not to treat?

If a woman is pregnant and chronic high blood pressure is seriously high, doctors typically don’t debate what to do. They treat it—and fast—mainly to minimize the risk for strokes and other potentially deadly cardiovascular events.

But what if the woman’s chronic high blood pressure is considered, well, mild—say, less than 160/105 mm Hg? As it happens, that’s the category the majority of pregnant women with hypertension fall into—and because of it, they risk myriad complications: preeclampsia, fetal death, preterm birth, poor fetal growth, and more.

Yet, for all those risks, doctors still don’t know with certainty what course of treatment, if any, to give in these cases. Anti-hypertensive medications may be of help to the women long-term, they say, but are they all that beneficial in the relatively short period of pregnancy, or even safe, for their developing babies? 

Pregnant woman at doctor's office having pressure measured.
High blood pressure is the most common medical problem during pregnancy. 
CREDIT: Jovanmandic, istockphoto

That’s the question NHLBI-funded Chronic Hypertension and Pregnancy (CHAP) Project is hoping to answer with a randomized, multicenter trial launched in 2014, involving over 2,400 pregnant women. Following strict safety protocols, the study is evaluating the benefits, effectiveness, and potential harms of using medication to treat mild chronic hypertension in pregnancy. 

The researchers, who still are recruiting participants, are also studying when best to deliver a baby to minimize the impact of conditions such as preeclampsia, that negatively affect both mother and child.

The results, the researchers say, can’t come soon enough.

“This question has been an elephant in the room for obstetric care providers and researchers for quite some time,” says Alan Tita, M.D., Ph.D., John C. Hauth, MD professor and vice chairman for research of obstetrics and gynecology in the University of Alabama at Birmingham’s School of Medicine and principal investigator for CHAP. “Everyone knows chronic hypertension causes serious and sometimes life-threatening complications for the pregnant woman and her baby, but no one really knows how best to manage the condition during pregnancy.”

“While we know chronic hypertension adversely affects the baby’s growth,” he adds, “there are concerns that treatment of hypertension may also impair the baby’s growth. It’s a catch-22, and it’s one for which we need to find answers.” 

Up to 6% of pregnant women in the United States suffer from chronic hypertension, but current guidelines from the American College of Obstetricians and Gynecologists (ACOG) recommend not giving anti-hypertensive medication to those with high blood pressure in the mild range—or less than 160/105 mmHg.

In the CHAP trial, one group of women is randomly assigned to receive anti-hypertensive medication, in order to bring their blood pressure to less than 140/90 mmHg, the recommended target for non-pregnant adults of reproductive age. The other group is treated according to ACOG’s guidelines.

“The problem is the majority of women with chronic hypertension at the reproductive age have mild chronic hypertension. We are talking about up to 80 percent of pregnant women with chronic hypertension who may not receive treatment, and we don’t know for certain whether that positively affects their pregnancy and whether that might lead to bad or good outcomes in the long term, compared with treatment,” Tita says.

In addition, the data that associates treatment with poor fetal growth is relatively weak, which is why investigating what works and what doesn’t in a rigorous trial is so important, Tita explains.

Known officially as hypertensive disorders of pregnancy, preeclampsia and gestational hypertension are among the leading causes of maternal illness and death worldwide, and for women who experience them, a host of future cardiovascular maladies for themselves and, perhaps, their children awaits.  

In a study of almost 59,000 women, NHLBI-funded researchers found that those who developed hypertensive disorders had higher rates of chronic high blood pressure, type 2 diabetes, and high cholesterol even decades after giving birth, than those with normal blood pressure during their first pregnancy.

“Studies have established consistent evidence that recognizes both preeclampsia and gestational hypertension as risk factors for cardiovascular disease in women,” says study author Jennifer Stuart, ScD, Associate Epidemiologist in the Division of Women's Health at Brigham and Women's Hospital and Harvard Medical School. “What remains less clear is how they get there. More specifically, what cardiovascular disease risk factors do they develop between the hypertensive pregnancy and the cardiovascular disease events, and when do they develop them? This information is critical to inform guidelines and direct prevention and screening efforts to reduce cardiovascular disease risk in these women.”

The researchers found that this relationship between having a history of preeclampsia or gestational hypertension and increased cardiovascular risk factors persisted, even after accounting for pre-pregnancy factors like body mass index, smoking, and family history. The researchers also noted that the women developed these risk factors sooner after pregnancy than their peers who had normal blood pressure in pregnancy.

It all begs key questions: Do hypertensive disorders of pregnancy contribute to the long-term higher risk of cardiovascular disease? “Or do they simply identify women who have ‘failed’ the cardiometabolic stress test of pregnancy because of a preexisting increased propensity for cardiovascular disease?,” asks Abigail Fraser, Ph.D., professor of Bristol Medical School, in an editorial about the study.

Answers to these questions are being explored through CHAP, Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-be Heart Health Study (nuMoM2b-HHS), and several other NHLBI-funded projects looking into pregnancy as a window to women’s cardiovascular health. How they get resolved could have significant practical implications, given that cardiovascular disease is the leading cause of death among women. 

For example, if hypertensive disorders of pregnancy alone increase the risks of cardiovascular disease—independent of a woman’s cardiovascular health before pregnancy—the prevention and treatment of such conditions could reduce the burden of cardiovascular disease in women.

“If, on the other hand, pre-pregnancy cardiovascular health is key, prevention efforts should be aimed at young women before conception,” Fraser writes.

While the research moves forward, experts say doctors and women should not just sit and wait.

It would be advisable that health care providers who treat women after pregnancy and through older age make themselves aware of the increased risk for diabetes, high cholesterol, and hypertension, and know that those risks emerge shortly after pregnancy and persist across decades, Stuart says.

“Doctors could obtain detailed pregnancy histories of their patients, capturing any history of preeclampsia or gestational hypertension,” she adds. “And women who have had any of these conditions should tell their doctors and adopt a heart healthy diet and lifestyle—just as they would if they had a family history of cardiovascular disease.”