Hypertension or diabetes before pregnancy linked to higher risk of fetal heart defects
· Medical Xpressedited by Sadie Harley, reviewed by Robert Egan
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Women with chronic hypertension (high blood pressure before pregnancy or diagnosed before 20 weeks of pregnancy) had a 30% higher risk of having a baby with critical congenital heart disease, the most severe form of heart defects, when compared to women with normal blood pressure before and during pregnancy, according to new independent, preliminary research presented at the American Heart Association's Scientific Sessions 2026, held Nov. 6–9 in Chicago.
High blood pressure during pregnancy is defined as systolic blood pressure (the top number) of 140 mm Hg or higher and diastolic blood pressure (the bottom number) of 90 mm Hg or higher. According to the American Heart Association/American College of Cardiology 2025 High Blood Pressure Guideline, high blood pressure affects approximately 16% of pregnancies. It is a leading cause of serious health complications and death for both pregnant individuals and their infants worldwide.
Types of high blood pressure in pregnancy that were included in this study were chronic (preexisting before pregnancy or diagnosed prior to 20 weeks of pregnancy); gestational (diagnosed at 20 weeks of pregnancy or later); chronic with gestational (high blood pressure before or during the first 20 weeks of pregnancy that continues to rise and/or leads to complications); and eclampsia (severe hypertension diagnosed after 20 weeks of pregnancy that includes seizures and other complications and requires emergency treatment).
This study explored maternal health factors to evaluate the potential association between high blood pressure-related disorders during pregnancy and the risk of critical congenital heart disease (CCHD), the most severe type of congenital heart disease, also called congenital heart defects. Infants with CCHD require surgery or catheter placement during the first year of life and continued cardiac specialty care.
The analysis found that maternal hypertension became increasingly common during the study period. The prevalence increased by nearly 48%—rising from approximately 9.4% of pregnancies in 2018 to 13.9% in 2024.
The prevalence of critical congenital heart disease also increased about 10% during the same time period, from 5.8 cases per 10,000 births in 2018 to 6.4 cases per 10,000 births in 2023–2024—representing nearly 4,000 infants in the U.S. each year.
"Our findings suggest that maternal heart health before and during pregnancy may have a particularly important relationship with fetal heart development," said study author Saad Ur Rahman, M.D., chief cardiology fellow in the division of cardiovascular medicine at Lahey Clinic of Beth Israel Lahey Health in Burlington, Massachusetts.
"These results emphasize the importance of monitoring blood pressure, discussing heart health with clinicians and receiving appropriate care before and during pregnancy to reduce the risk of fetal heart defects."
Study's main findings:
- Out of more than 44 million live births in the U.S. from 2018–2024, nearly 28,000 infants (0.06%) were diagnosed with critical congenital heart disease. Approximately 1.5% of the cases were linked to chronic or gestational hypertension.
- Chronic hypertension during pregnancy was associated with a 30% higher risk of critical congenital heart disease for the infant, compared to infants born from pregnancies where the mother did not have any type of high blood pressure.
- Women with either type 1 or type 2 diabetes prior to pregnancy had a 48% increased risk of having babies with severe heart defects compared to women without diabetes.
- Women who developed gestational hypertension had an 8% increased likelihood of having babies with critical congenital heart disease.
- Eclampsia was not significantly associated with critical congenital heart disease.
"Future studies should explore the biological mechanisms that may explain the link between maternal high blood pressure and CCHD, as well as examine whether CCHD risk is influenced by the timing, severity and treatment of high blood pressure during pregnancy," said Rahman.
"This study adds to a growing body of evidence linking maternal health and the intrauterine environment with fetal cardiovascular development," said Flora Nuñez Gallegos, M.D., M.P.H., a pediatric cardiologist at University of California San Francisco and a member of the American Heart Association's Council on Lifelong Congenital Heart Disease and Heart Health in the Young (the Young Hearts Council).
"Although the absolute risk of critical congenital heart disease remains low, these findings highlight the importance of identifying and managing chronic hypertension before and during pregnancy. The association with an infant's risk of critical congenital heart disease was stronger for chronic hypertension than for gestational hypertension, emphasizing the importance of maternal health even before pregnancy begins."
Study details, background, design and limitations:
- The study used the CDC's National Vital Statistics System (NVSS) U.S. Natality Public Use Files, a nationwide database of U.S. birth-certificate records of over 44 million live births from 2018 through 2024.
- Categories of blood pressure disorders during pregnancy detailed in this study included: no hypertension, chronic hypertension, gestational hypertension, chronic plus gestational hypertension, and eclampsia.
- Analyses accounted for and adjusted for other individual factors, such as maternal demographics, type 1 or type 2 diabetes, smoking status, pregnancy history and pregnancy length.
- The study authors noted that the observational design limits conclusions to identifying associations rather than direct causation between chronic hypertension and CCHD.
- Another limitation is that the study used national birth certificate data, which does not capture several factors that may influence the results. These include genetic factors, maternal health history, prenatal imaging, the timing of high blood pressure during pregnancy, whether blood pressure treatment was received, how well blood pressure was controlled during pregnancy, and how consistently and for how long treatment was followed.
Key medical concepts
Hypertension, Pregnancy-InducedDiabetes Type 1Diabetes Type 2
Clinical categories
Obstetrics & gynecologyCardiologyPregnancyWomen's healthCommon illnesses & Prevention Provided by American Heart Association Who's behind this story?
Sadie Harley
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Robert Egan
Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →
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