Higher blood pressure before pregnancy may increase miscarriage risk

"Elevated blood pressure among young adults is associated with a higher risk of heart disease later in life, and this study suggests it may also have an effect on reproductive health," said Carrie J. Nobles, Ph.D., lead author of the study and a postdoctoral fellow in the Epidemiology Branch of the Eunice Kennedy Shriver National Institute for Child Health and Human Development (NICHD) in Bethesda, Maryland.

The study -- which cannot reach a cause-and-effect conclusion -- is the first to look at preconception blood pressure and reproductive outcomes in healthy women not diagnosed with high blood pressure or heart disease.

Researchers studied 1,228 women (average age 28.7 years, 95 percent white) who had already experienced 1-2 pregnancy losses and were currently trying to become pregnant. The women were part of a clinical trial to determine whether taking low-dose aspirin might reduce the risk of miscarriage.

During the study, women had their blood pressure measured when they were trying to become pregnant and again during early pregnancy. Average blood pressure prior to pregnancy was 111.6 mm Hg /72.5 mm Hg. Of the 797 women who conceived within six months, 24 percent suffered a pregnancy loss.

Researchers also found:

• Every 10-point increase in diastolic blood pressure (lower number) was associated with an 18 percent increased risk of pregnancy loss.
• Every 10-point increase in mean arterial pressure (an average of the lower and higher numbers) was associated with a 17 percent increased risk of pregnancy loss.
• The findings were similar for preconception and early-pregnancy blood pressure.

"The impact of cardiovascular risk factors starts really early in life. Physicians treating women of reproductive age should pay attention to slightly elevated blood pressure because it may have other not-well-recognized effects, such as adverse pregnancy outcome," said Enrique F. Schisterman, Ph.D., senior author of the study and Senior Investigator and Chief of the Epidemiology Branch of NICHD. "Preconception is a previously unrecognized critical window for intervention such as lifestyle changes that can help prevent later heart disease and may also improve reproductive health."

Whether women had been randomly assigned to take low-dose aspirin as part of this clinical trial (Effects of Aspirin in Gestation and Reproduction) made no difference in the impact of blood pressure on pregnancy loss, the researchers found.

Because the study was conducted in women who already had experienced a miscarriage, it is unclear whether the results can be generalized to all young women. Additionally, the study was mostly composed of white participants, and further research is needed to ensure the results apply to women of different races.