Pregnant women diagnosed with chronic hypertension, or persistent high blood pressure, are more at risk for pregnancy-related complications, maternal death and adverse outcomes for their newborns. Researchers at Rutgers Robert Wood Johnson Medical School sought to understand trends in hypertension for pregnant women over time, and how it might relate to obesity and smoking, which are often causes of high blood pressure.

The study looked at more than 151 million pregnant women in the US between 1970 and 2010, using data from the National Hospital Discharge Survey, which is believed by researchers to be representative of all pregnant women in the US during that time. Maternal age, year of delivery (period) and maternal year of birth (birth cohort), as well as race were examined as risk factors for chronic hypertension.

Results showed that rates of hypertension increased 13-fold between 1970 and 2010, with black women having more than twice the rate of white women in any given year. While obesity and smoking are proven risk factors for hypertension, the growing prevalence of obesity and the declining prevalence of smoking during pregnancy had virtually no impact on the increase of national trends found in the study, surprising researchers. Instead, advancing maternal age and year of delivery were factors strongly associated with increasing trends. The rate of chronic hypertension increased sharply with advancing maternal age and period from 0.11% in 1970 to 1.52% in 2010. The rate of hypertension increased, on average, by 6% per year, 13 times what it was in 1970.

Interestingly, the authors also report substantial race-disparity in the prevalence of chronic hypertension. The racial disparity in hypertension could be because black women also suffer from hypertension-related complications such as higher rates of preeclampsia, pregestational and gestational diabetes, preterm delivery and perinatal mortality. Prior research has shown that compared with white women, black women have higher rates of obesity, are more likely to smoke and use drugs and are at greater social disadvantage, all of which may contribute to an increased risk of chronic hypertension.

Lead author Cande V. Ananth, PhD, MPH, professor and vice chair of academic affairs, and chief of the Division of Epidemiology and Biostatistics in the Department of Obstetrics, Gynecology and Reproductive Sciences, explains why hypertension rose by period, stating, “Better prenatal care in recent years may have caught hypertension earlier, as well as different diagnostic criteria.” Despite these potential reasons for increased hypertension over time, there are still strong maternal age correlations. “Women are having children later—4-5 years older, on average, now than in the 70’s and 80’s—and are experiencing higher rates of hypertension during pregnancy as a result,” says Dr. Ananth.

Because the the study found that the biggest contributors of hypertension are age and time period—factors that will most likely not change—the question then becomes, how can individuals lesson the growing rates of hypertension, and subsequently lower the adverse outcomes in pregnancy?

Dr. Ananth suggests, “Women need to better control their blood pressure before and during pregnancy. Smoking cessation, weight control, behavioral changes and effective anti-hypertensive therapy,—all modifiable factors—may lead to healthier lifestyle, and will likely have a substantial beneficial effect on chronic hypertension and pregnancy outcomes.”

While the best outcome would be to control hypertension before becoming pregnant, Dr. Ananth suggests that women can lower their blood pressure by reducing obesity, quitting smoking, adopting an overall healthier lifestyle before and during pregnancy, and treating high blood pressure effectively. Further, obese women do not need to gain much weight during pregnancy, and for every 1-2 lbs. lost prior to pregnancy, blood pressure is reduced.

“Not only do these findings have implications for the health of the women and newborns during pregnancy, they have lasting implications on future risks of cardiovascular and stroke risks in women later in life. Being aware of your blood pressure before and during pregnancy, and taking steps to reduce it, is key to women’s health during pregnancy,” says Dr. Ananth.