Blood Pressure Patterns During Pregnancy Predict Later Risk of High Blood Pressure

Women whose blood pressure levels during pregnancy fall within the range considered clinically normal, but whose blood pressure does not decrease during pregnancy, are at increased risk of developing hypertension in the five years following childbirth. These women – about 12% of the studied population – would not be classified as high-risk patients under current medical guidelines, but the new findings could help identify them as candidates for early intervention. The results of the study were published in the Journal of the American College of Cardiology: Advances.

Blood Pressure Patterns During Pregnancy and Cardiovascular Disease

The researchers, who were partially funded by the National Institutes of Health, collected data on blood pressure and other health factors from 854 women during pregnancy and up to five years after childbirth. This longitudinal approach allowed them to track women’s blood pressure levels throughout pregnancy and establish a link between certain blood pressure patterns and high blood pressure several years later.

For most women in the study (80.2%), systolic blood pressure remained low throughout pregnancy. For 7.4% of women, blood pressure was initially high, then dropped in the second trimester and rose again afterwards. A third group of women (12.4 %) had slightly elevated systolic blood pressure that remained at a healthy level throughout pregnancy but did not drop in the second trimester. Compared to the first group, these women had a 4.91 times higher risk of developing hypertension in the five years after childbirth. “This group of women would not be identified as being at higher long-term risk for hypertension by any of the current clinical criteria, as their blood pressure remained below the diagnostic thresholds and most had no other traditional risk factors,” said Dr. Shohreh Farzan, associate professor of population and health sciences at the Keck School of Medicine at USC and senior author of the study.

“The findings suggest that monitoring blood pressure patterns during pregnancy could help identify this overlooked group and plan for interventions that could prevent cardiovascular disease,” said Zhongzheng (Jason) Niu, PhD, study first author, Presidential Sustainability Solutions Fellow at USC and assistant professor of epidemiology and environmental health at the University at Buffalo.

An Unexpected Risk

The data for the study comes from the Maternal and Developmental Risks from Environmental and Social Stressors (MADRES) cohort, a group of 854 low-income Hispanic women and their children that researchers at the Keck School of Medicine have been working with since 2015. Researchers collected data on demographics, lifestyle factors and various health indicators regularly during pregnancy and at annual visits for up to five years after birth.

After collecting the data, researchers used a statistical approach known as latent class growth modeling to look for patterns in the women’s blood pressure levels over the course of their pregnancies and see if those patterns were associated with changes in their health status at later visits. They found three distinct patterns of systolic blood pressure during pregnancy: 80.2% of women had consistently low blood pressure; 7.4% of women had high blood pressure that dropped in the second trimester; and 12.4% of women had slightly elevated blood pressure without dropping in the middle of pregnancy.

The group with high blood pressure and a drop in blood pressure in the middle of pregnancy had classic high-risk pregnancies, including more cases of preeclampsia and gestational hypertension than in the other two groups. These women also had a 5.44 times higher risk of high blood pressure in the five years following the birth than the group with the lowest blood pressure. The 12.4% of women with slightly elevated blood pressure but no drop in blood pressure in mid-pregnancy had an almost equally high risk of developing high blood pressure later on – 4.91 times higher than that of the group with the lowest blood pressure. However, because these women had no traditional risk factors, they were not made aware of their higher risk, nor were they monitored closely for the development of high blood pressure.

Simple Changes in Clinical Practice Could Help Identify High-Risk Groups

These findings come at a time when both the American Heart Association (AHA) and the American College of Obstetricians and Gynecologists are increasing their focus on women’s heart health. After presenting the results at the AHA EPI|Lifestyle meeting in 2023, Niu was awarded the organization’s Trudy Bush Fellowship for research into women’s health cardiovascular disease. The study is one of the first to analyze high blood pressure between pregnancy and menopause, an area that has long been neglected by medical research.

Women’s health can change dramatically between pregnancy and menopause, but it is a period about which little is known. According to the researchers, their study is important to close this knowledge gap regarding high blood pressure. Simple changes in clinical practice could help identify and manage this high-risk group. Doctors can monitor blood pressure throughout pregnancy and follow up with women who don’t show a drop in the second trimester, even if their numbers remain in the normal range. The AHA, which updated the high blood pressure limits for the general population in 2017, may also consider adjusting its guidelines for blood pressure during pregnancy.

More studies are needed to replicate the findings and learn more about women in both risk groups. Farzan, Niu and their colleagues are also investigating whether environmental exposures – including air pollution, heavy metals and per- and polyfluoroalkyl substances (PFAS) – are associated with changes in blood pressure patterns during and after pregnancy.