Study Suggests Strict Hypertension Control Best During Pregnancy

By Gene Emery

NEW YORK (Reuters Health) - When it comes to controlling mild-to-moderate hypertension during pregnancy, tighter seems to be better.

A comparison of 497 women whose diastolic blood pressure goal was 100 mm Hg were no more likely to lose their fetus or require high-level neonatal care for more than 48 hours during the first 28 days after birth than 490 women whose goal was 85 mm Hg.

But allowing higher blood pressures posed a serious risk to the mother, increasing the likelihood of stroke, chief author Dr. Laura Magee, a researcher at the Child & Family Research Institute and the University of British Columbia, in Vancouver, told Reuters Health in a telephone interview.

"There was no benefit for the baby" with less-strict blood pressure control, she said. "So I can't offer a benefit, yet I know I'm entertaining a risk of severe hypertension to the mother. And there was nothing in the numbers to suggest the mothers did better" if blood pressure control was less aggressive.

Dr. Magee had been an advocate for looser control, believing as many other doctors do that lowering blood pressure might pose a hazard by reducing the flow of blood to a baby. But the results, published online January 28 in the New England Journal of Medicine, made her a believer in tighter control, she said.

The study appears amid ongoing debate over the best blood pressure target for pregnant women, 5% to 6% of whom will develop gestational hypertension without proteinurea. Two percent of women develop preeclampsia.

Dr. Magee estimated that the number of physicians who advocate for tight control and less-tight control is evenly split.

With the new findings, she said, "probably half are saying 'I was right all along' and half are saying 'That's not how I thought it would turn out.'"

The women enrolled at 94 sites in 15 countries had diastolic blood pressure of 90 to 105 mm Hg (or at least 85 mm Hg if they were already on hypertensive medication) and their fetus was between 14 and 33 weeks of gestation.

In the tight-control group, 30.7% of the women had a pregnancy loss or needed at least two days of high-level neonatal care, compared to 31.4% of the women in the less-tight group, with an odds ratio of 1.02.

The rates for serious maternal complications were 2.0% for tight control versus 3.7% for less-tight control, a difference that was not statistically significant, even though women in the less-tight group were far more likely to have severe hypertension.

Among women whose blood pressures could be higher, 40.6% had blood pressure of at least 160/110 mm Hg versus 27.5% women whose pressure was under tight control.

In addition, women in the less-tight-control group were less likely to take their blood pressure medicine. Their rate of compliance was 73.4% versus 92.6% in the tight-control group (p<0.001).

In a Journal editorial, Dr. Caren Solomon and Michael Greene, of the Massachusetts General Hospital, said the study shows that "tight control of hypertension conferred no apparent benefits to the fetus and only a moderate benefit (a lower rate of progression to severe hypertension) for the mother. It does, however, provide valuable reassurance that tight control, as targeted in this study, does not carry major risks for the fetus or newborn."

An assessment of the economic costs and benefits of each strategy is under way, Dr. Magee said.

"Our hypothesis was that medical costs would be driven by the baby's care or maternal hospitalization. But because there was no significant difference between the two, we don't think the difference will be a large one," she said.

The study was known as CHIPS - Control of Hypertension in Pregnancy Study.

This research was supported by the Canadian Institutes of Health Research. One author reports receiving research support Alere International for the study of preeclampsia; no other authors report any disclosures.

SOURCE: https://bit.ly/1z45D1n

N Engl J Med 2015.

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