New US research has found that the rate of high blood pressure among pregnant women age 35 and over in the United States is on the increase, and black women are at an even higher risk of the condition than white women.
Carried out by researchers at Rutgers Robert Wood Johnson Medical School, the new study looked at the pregnancies of more than 151 million women in the United States between 1970 and 2010 to investigate the rates of hypertension (high blood pressure) among pregnant women during this period.
The researchers looked into how changes in obesity and smoking may be associated with the rate of high blood pressure, and also how factors such as maternal age, the year of delivery, and race could affect the risk for hypertension.
The findings, published in the journal Hypertension, showed that the rate of high blood pressure among pregnant women in the US has increased by more than 75 percent since 1970, increasing on average by six percent each year.
Moreover, rates of high blood pressure among black women were more than two times higher than among white women.
The researchers also found that although obesity and smoking are proven risk factors for high blood pressure, they actually had no impact on the increasing rate of hypertension in the US during the past four decades.
Instead, advanced maternal age appeared to be the factor associated with the increased rate, said lead author of the study Cande V. Ananth.
"Women are having children later -- 4 to 5 years older, on average, now than in the 1970s and 1980s -- and are experiencing higher rates of hypertension during pregnancy as a result," he added.
As to why black women appear to be at a higher risk than white women for developing high blood pressure during pregnancy, Ananth and his team say this could be because black women have higher rates of preeclampsia, pregestational and gestational diabetes, preterm delivery and perinatal mortality. Previous research has also 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 are factors that may contribute to an increased risk of hypertension.
Ananth noted that as the increasing age of pregnant women will probably not change, then women can change various lifestyle factors to help to modify their risk hypertension, which can help prevent possible adverse outcomes in pregnancy.
"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," Ananth said.
"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," he said.