New research has discovered that the rate of high blood pressure among pregnant women aged 35-years-old and over is on the rise over the last 40 years.
The study also found that black women are at a far higher risk of the condition than white women.
Rutgers Robert Wood Johnson Medical School looked at the pregnancies of over 151 million women in America between 1970 and 2010 to analyse rates of hypertension (high blood pressure).
Researchers also examined changes in obesity and smoking in association with rates of high blood pressure, and investigated factors such as maternal age, year of birth and race.
The findings have been published in the journal 'Hypertension', and illustrated that the rate of high blood pressure among pregnant women in the US has increased by more than 75 percent since 1970, rising on average by six percent each year.
Shockingly, rates of high blood pressure among black women were more than two times higher than among white women. Scientists couldn't locate a link between the increasing rate of hypertension and obesity and smoking.
Advanced maternal age seemed to be the factor associated with the increased rate, according to the study's lead author, Cande V. Ananth.
"Women are having children later - four to five 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.
Ananth and his team say that the higher rates of high blood pressure during the pregnancies of black women could be because black women have higher rates of preeclampsia, pregestational and gestational diabetes, preterm delivery and perinatal mortality.
Unfortunately, black women have higher rates of obesity, are more likely to smoke and use drugs, and are at greater social disadvantage. These factors can contribute to increased risk of hypertension.
The increasing age of pregnant women is unlikely to change, but women can alter parts of their lifestyle to reduce the risk of hypertension.
"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."