Dallas, Texas - The number of women with high blood pressure (HBP) when they become pregnant or who have it diagnosed during the first 20 weeks of pregnancy has spiked in the United States over the last four decades, especially among black women, according to new research in the American Heart Association’s journal Hypertension.

Having high blood pressure before becoming pregnant and during pregnancy poses potential complications for both women and their unborn children, including increased risks of stillbirth or infant death and preeclampsia (life-threatening high blood pressure during pregnancy), stroke, heart failure, cardiomyopathy (heart muscle disease) or kidney failure and death among other risks for the mother.

The researchers defined high blood pressure as 140 mm Hg systolic blood pressure and 90 mm Hg diastolic blood pressure over the course of the study, however, the American Heart Association defines high blood pressure as 130mm Hg systolic blood pressure (the top number in a blood pressure reading) and 80 mm Hg diastolic blood pressure (the bottom number in a blood pressure reading).

“Women who already have high blood pressure and are planning to become pregnant should work closely with their health care provider to closely monitor and manage their blood pressure, especially during pregnancy, to reduce the serious health risks to both themselves and their unborn child,” said lead study author Cande V. Ananth, Ph.D., M.P.H., professor and chief of the Division of Epidemiology and Biostatistics in the Department of Obstetrics, Gynecology and Reproductive Sciences at Rutgers Robert Wood Johnson Medical School in New Brunswick, New Jersey.

In this study, the largest of its kind according to the researchers, the rates of chronic high blood pressure in pregnant women aged 15 to 49 years were evaluated. Chronic high blood pressure was defined as having high blood pressure before becoming pregnant or during the first 20 weeks of pregnancy. Using data from the Center for Disease Control’s National Hospital Discharge Survey (NHDS), they analyzed close to 151.5 million childbirth-related hospitalizations from 1970 to 2010 for changes in chronic hypertension, considering factors such as the mother’s age, year of delivery and race.

Overall, the researchers found that almost 1 million (0.63%) women in the study experienced chronic high blood pressure during their pregnancy, and the rate increased sharply with the mother’s age and year of delivery, shooting up from 0.11% in 1970 to 1.52% in 2010—over a 13-fold increase over the past four decades.

“We found that mothers who were older when they became pregnant were more likely to have chronic hypertension,” said Ananth. “Since more women are electing to postpone their first pregnancies, and advanced maternal age is strongly associated with chronic high blood pressure, women should be aware of the risks associated with having high blood pressure during pregnancy.”

The results also revealed that chronic high blood pressure during pregnancy:

• Affected black women at more than twice the rate of white women.
• Increased on average by 6% every year since 1979, with white women showing a slightly higher increase (7%) than black women (4%) each year.

“We originally speculated that the disproportionately higher rates of obesity, smoking, diabetes and vascular disease among black women might explain these racial disparities,” said Ananth. However, after adjusting for obesity and smoking rates, the researchers determined that these factors did not influence the upward trend of chronic high blood pressure during pregnancy.

“We were a very surprised that the increasing prevalence of obesity and the declining prevalence of smoking rates had virtually no impact on trends in chronic hypertension during pregnancy,” said Ananth. Despite these results, obesity and smoking remain strong risk factors for high blood pressure.

An editorial “Trends in Chronic Hypertension in Pregnancy Highlight Racial Disparities in Maternal Health,” will also be published in the same issue of Hypertension.

Co-authors of this study are Christina M. Duzyj, M.D., M.P.H.; Stacy Yadava, M.D.; Marlene Schwebel, J.D., A.P.N.; Alan T.N. Tita, M.D., Ph.D.; K.S. Joseph, M.D. Ph.D. Author disclosures are on the manuscript.