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Women who develop high blood pressure during pregnancy may have fewer associated complications if obstetricians routinely induce labor once the pregnancy has exceeded 37 weeks gestation, according to Dutch researchers.

HYPITAT, a multicenter study of 756 pregnant women who developed gestational hypertension or mild preeclampsia, found that 31% of the women who were induced had a poor outcome versus 44% of the women who had expectant monitoring.

The difference of 49 women was significant (P<0.0001), wrote Corine M. Koopmans, MD, of University Medical Centre in Groningen, and colleagues. The findings were published online in The Lancet.

“We believe that induction of labor should be advised for women with gestational hypertension and a diastolic blood pressure of 95 mmHg or higher or mild preeclampsia at a gestational age beyond 37 weeks,” Koopmans wrote.

The authors said the finding underscored the importance of “frequent blood pressure monitoring during the concluding weeks of pregnancy.”

They noted that the finding had implications for the U.S. and other developed nations where induction of labor in women with these conditions is common practice. But “until now, this recommendation has not been based on the results of randomized clinical trials,” they said.

The women with singleton pregnancies were recruited at six academic medical centers and 32 nonacademic hospitals from October 2005 through March 2008. All women were at 36 to 41 weeks’ gestation and all had gestational hypertension or mild preeclampsia.

The women were randomized 1:1 to induction of labor or expectant monitoring. The primary endpoint was a composite measure of poor maternal outcome.

That measure included maternal mortality and maternal morbidity — specifically, HELLP syndrome (hemolytic anemia, elevated liver enzymes, and low platelet count), pulmonary edema, thomboembolic disease, and placental abruption — as well as progression to severe hypertension or proteinuria, and/or loss of more than 1,000 mL blood due to postpartum hemorrhage.

In the induction group, 117 of the 377 women reached the composite primary outcome versus 166 of the 379 controls.

There was, however, no cases of maternal or neonatal death in either group, and the difference in outcomes was primarily driven by a difference in blood pressure.

Only 55 women who were induced developed severe systolic hypertension, while 62 had diastolic pressures above normal. In the control group, 88 women developed systolic hypertension and 103 had severe elevations in diastolic pressure, for an absolute risk reduction of 8.63% for systolic and 10.73% for diastolic hypertension.

There were fewer cesarean sections in the induced group, 54 versus 72, but this difference was not statistically significant.

In a commentary published with the HYPITAT results, Donna D. Johnson, MD, of the Medical University of South Carolina, said one concern about the study design was the inclusion of women at 36 weeks’ gestation.

“Although serious neonatal complications are uncommon, late preterm birth can adversely affect the neonate,” she wrote. “In a subgroup analysis, composite maternal morbidity was not improved by induction of labor at this gestational age (36-37 weeks).”

She pointed out that while the study was not powered to detect differences at each gestational age “we should be hesitant to induce labor in women before 37 weeks of gestation for mild preeclampsia or gestational hypertension.”

The trial was funded by ZonMw, the Netherlands organization for health research and development, program Doelmatigheidsonderzoek. Koopman and co-investigators declared no conflicts of interest. Johnson declared that she had no conflicts of interest.

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