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New Research Recommends Treating Elevated Blood Pressure During Pregnancy

Last Updated on Wednesday, February 11, 2015

Throughout her career in Canada and the UK, Dr. Laura Magee has taken a restrained approach to the use of blood pressure-lowering medication in her pregnant patients, fearing that lowering pressure could reduce the flow of blood and vital nutrients to their babies.

But Magee, a researcher at the Child & Family Research Institute (CFRI) and the University of British Columbia (UBC), and a physician at BC Women’s Hospital and Health Centre, an agency of the Provincial Health Services Authority (PHSA), has up-ended her own beliefs with an international study published in late January in the New England Journal of Medicine.

Called CHIPS, for Control of Hypertension in Pregnancy Study, the 15-country study shows that treating a woman’s elevated blood pressure during pregnancy is safer for her, and safe for her baby. As a result of these findings, Magee and her collaborators recommend normalizing blood pressure in pregnant women.

“Before this study, I was a ‘less tight’ controller,” Magee says. “I was hoping that this approach would be better for the baby, without increasing risks for the mother. However, I was wrong. ‘Less tight’ control, which means allowing blood pressure to be mildly to moderately elevated in pregnancy, is not better for the baby. It’s actually harmful to the mother, who will more often experience levels of blood pressure that increase the risk of stroke. As a responsible maternity care provider, I can no longer justify a ‘less tight’ approach to blood pressure control.”

The study, which tracked the health of 987 women and their newborns at 94 sites around the world, addresses an age-old belief that reducing elevated blood pressure during pregnancy might lead to reduced growth in the womb and worse health at birth for the baby.

But normalizing a pregnant women’s elevated blood pressure did not result in poorer outcomes for babies before or after birth. At the same time, allowing the mother’s blood pressure to be mildly to moderately elevated in pregnancy led to more episodes of dangerously elevated blood pressure that increase the risk of stroke and death for the mother during pregnancy.

“The CHIPS trial is a landmark study that should begin to change the trajectory of care for women with hypertension in pregnancy,” said Dr. Thomas Easterling, Chair of the Preeclampsia Foundation Medical Advisory Board. “Current recommendations in the United States suggest withholding antihypertensive therapy from pregnant women until blood pressures have reached severe range (≥160/105 mmHg) due to concerns for the baby and lack of perceived benefit to the mother. The CHIPS trial suggests that controlling blood pressure with a target diastolic blood pressure (the lower number) of 85 mmHg reduces the risk for severe hypertensive disease without adversely affecting the baby – and in particular – fetal growth. Pregnant women developing hypertension should discuss these findings with their providers to determine, in partnership, their individual goals for blood pressure control.”

About the study:
• The CHIPS Trial (Control of Hypertension in Pregnancy Study) was designed to study the impact of ‘less tight’ or ‘tight’ control of high blood pressure during pregnancy on outcomes for the baby and for the mother.
• 987 women participated between 2009 and 2012 at 94 study sites in 15 countries.
• Women participating were between 14 and 33 weeks pregnant. They were randomly assigned to one of two groups. A group of 497 women had ‘less tight’ control with a target diastolic blood pressure of 100 mmHg, while the second group of 490 women had ‘tight’ control with a target diastolic blood pressure of 85 mmHg.
• Most of the women in both groups received blood pressure medication at some point in the trial (77 percent in the ‘less tight’ group and 94 percent in the ‘tight’ control group).
• Severe hypertension developed in 40.6% of women in the less tight control group compared to 27.5% in the tight control group. 4.3% of women in the less tight group developed a platelet count <100,000/mL compared to 1.6% in the tight control group.
• The researchers found that the number of babies who died or were admitted for prolonged newborn intensive care was similar between the two blood pressure control groups. Fetal growth was also similar.
• The study was funded by the Canadian Institutes of Health Research.

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