Rate of pregnancy-related high blood pressure disorders on the rise

Pregnancy complications among individuals between the ages of 15 and 44 are increasing dramatically, a new Northwestern Medicine study has found.

The rate of high blood pressure-related disorders among pregnant individuals more than doubled over a recent 12-year period, from 38.4 per 1,000 live births in 2007 to 77.8 in 2019, according to the study.

The large study, which included data from the National Center for Health Statistics Natality Files from 2007 to 2019, which includes all live births in the U.S. (51.6 million births), found the rate of increase accelerated in more recent years, growing 9.1% a year on average from 2014 to 2019 compared to 4.1% a year from 2007 to 2014.

“The increase in pregnancy complications is alarming because these adverse pregnancy outcomes— including hypertension in pregnancy, preterm birth and a low birth-weight infant—not only adversely influence both mom and child in the short-term, but for years to come,” said corresponding study author Dr. Sadiya Khan, assistant professor of cardiology and epidemiology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician.

Since pregnancy complications such as high blood pressure are linked to a long-term risk of heart disease, these findings fill in important details about women’s heart health during a crucial period of their lives, said lead study author Dr. Priya Freaney, an advanced cardiovascular fellow at Feinberg.

“Pregnancy can serve as a crystal ball for us to look into what may happen in the future for a woman’s cardiovascular health,” Freaney said.

The average age of women giving birth increased from 27.4 in 2007 to 29.1 years in 2019. But despite much attention often focusing on mothers of advanced maternal age (35 years old and up), the relative increase in problematic pregnancies was higher in younger women, the scientists said.

“This suggests that increasing maternal age is not the only driver in these unfavorable trends, and that we have to look into some of the other reasons for that," Freaney said.

The scientists analyzed rates of three types of adverse pregnancy outcomes that account for many of the health complications pregnant individuals and their children experience: low birth weight, preterm deliveries and hypertensive disorders of pregnancy. The third category includes preeclampsia and gestational hypertension, which are forms of high blood pressure during pregnancy. The study found one in five births resulted in one of these three adverse pregnancy outcomes: a pregnancy-related high blood pressure disorder, a preterm delivery or a baby with low birth weight.

Increases were similar across all age, racial and ethnic groups, which means there has not been a narrowing of previously established disparities between Black and white mothers. 

“We want the takeaway from our study to increase awareness among clinicians (physicians and midwives) who care for pregnant individuals and the public, including women who may be thinking of becoming pregnant, are pregnant or had one of these complications during pregnancy,” Khan said. “While these complications can be life-threatening, early identification and intervention can be life-saving.” 

The study also charted rates of preterm birth and babies with low birth weight. The higher rates in 2019, though slight, reversed a downward trend seen in 2014. 

A new and important finding is that both the unfavorable trends in low birth weight and preterm birth appear to be driven by the increase in blood pressure issues during pregnancy, Freaney said. A woman with preeclampsia might need to be induced early, which would lead to a preterm delivery. A baby born early is more likely to have a low birth weight.

"The reason for these increases still needs to be studied further and is likely multifactorial, but important contributors may include worsening pre-pregnancy cardiac health, poor diet, suboptimal perinatal care and potentially an increase in rates of detection,” Freaney said. “This further emphasizes the need for us to develop targeted interventions to predict, prevent and manage hypertensive disorders of pregnancy in order to reverse these trends and improve women’s heart health.”

Freaney said the findings also highlight the need for women to be taught about the long-term implications of high blood pressure during pregnancy. She said women who experienced high blood pressure during pregnancy should know that "even if your blood pressure goes back to normal after your pregnancy, it should still be seen as a warning sign and an important topic to be discussed with a doctor about how to optimize your heart health and prevent cardiovascular disease in the future."

Other Northwestern study authors include Dr. Donald Lloyd-Jones, Dr. Norrina Allen, Dr. Phillip Greenland, Dr. Michael Wang, Dr. Amanda Perak, Dr. Rebecca Molsberry and Dr. Katharine Harrington.