When pregnant women have high blood pressure, more-intensive treatment doesn't seem to affect their babies, but it may lower the odds that the moms will develop severely high blood pressure.
That's the conclusion of a clinical trial reported in the New England Journal of Medicine.
Experts were divided, however, on how to interpret the results.
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For one of the study's authors, the choice is clear. Tighter blood pressure control, aiming to get women's numbers "normalised", is better, said the study's lead researcher, Dr. Laura Magee, of the Child and Family Research Institute and the University of British Columbia in Vancouver, Canada.
"If less-tight control had no benefit for the baby, then how do you justify the risk of severe (high blood pressure) in the mother?" said Magee.
International guidelines vary
But current international guidelines on managing high blood pressure in pregnancy vary. And the advice from the American College of Obstetricians and Gynaecologists (ACOG) is consistent with the "less-tight" approach, according to Dr. James Martin, a past president of ACOG.
To him, the new findings support that guidance. "Tighter blood pressure control doesn't seem to make much difference," said Martin, who recently retired as director of maternal-foetal medicine at the University of Mississippi Medical Centre.
"This basically suggests we don't have to change what we're already doing," Martin said.
Most common medical condition
High blood pressure, or hypertension, is the most common medical condition of pregnancy – affecting about 10 percent of pregnant women, according to Magee's team.
Some of those women go into pregnancy with the condition, but many more develop pregnancy-induced hypertension, which arises after the 20th week.
Magee said the long-standing question has been whether doctors should try to "normalise" women's blood pressure numbers – as they would with a patient who wasn't pregnant – or be less aggressive.
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The worry, Martin explained, is that lowering a pregnant woman's blood pressure too much could reduce blood flow to the placenta and impair foetal growth. Some studies have found that to be a risk.
But in this trial, the degree of blood pressure control did not affect a woman's risk of pregnancy loss or having a baby who needed a stay in the new-born intensive care unit, Magee said.
The findings are based on nearly 1,000 pregnant women from 16 different countries who had high blood pressure. Half were randomly assigned to "tight" blood pressure control, and half to "less tight".
High blood pressure is defined as above 140/90 mm Hg. For the tight-control group, the goal was to get that second number (the diastolic pressure) to 85 or lower; for the less-tight group, the goal was 100 or lower, according to the study.
Treatment involved regular blood pressure checks and, for most women, medication – with the dose adjusted when needed. Usually, women took a drug called labetalol, which is the blood pressure medication most commonly used during pregnancy.
In the end, Magee's team found no differences in how the two groups fared, except for one: Almost 41 percent of women under looser blood pressure control eventually developed severe high blood pressure (a reading of 160/110 mm Hg or higher), while just 27.5 percent of women on the tighter regimen developed severe high blood pressure.
Severe high blood pressure can generally be quickly brought down with IV medication, Martin said. The main concern is that it can lead to a stroke in some women.
But, that didn't happen in this trial to women with higher blood pressure. However, one woman on the stricter treatment regimen had a stroke.
Martin noted that the less-aggressive approach can be easier for women, with less blood pressure monitoring at home and the doctor's office.
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However, Magee said she believes the risk of severely high numbers is not acceptable if less-intensive treatment has no clear benefit for babies.
"Before this study, I was for less-tight control," she noted. "Now I've changed my practice."
Until now, studies on this issue have been small or lower-quality, according to Magee. She said current professional guidelines vary because of that lack of strong evidence.
For now, both Magee and Martin encouraged pregnant women with high blood pressure to keep up with their doctor visits and stick with a treatment plan. But Magee suggested advocating for tighter blood pressure control.
Chronic hypertension and pregnancy project
She noted that more evidence on the issue will be coming. Another major clinical trial – called the Chronic Hypertension and Pregnancy Project – is set to get underway in U.S. hospitals soon.
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