Chronic hypertension before or during pregnancy increases the risk of a baby being born with a critical congenital heart disease by 30%, according to a new analysis of more than 44 million U.S. live births. “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,” said Saad Ur Rahman, M.D., chief cardiology fellow at Lahey Clinic of Beth Israel Lahey Health.
This research, to be presented at the American Heart Association’s Scientific Sessions 2026, provides a large-scale look at the link between maternal hypertensive disorders and severe fetal heart defects. The study’s findings are considered preliminary as the abstract has not undergone peer review, but the sheer volume of data analyzed offers a powerful new perspective on a critical public health issue. The analysis revealed a clear hierarchy of risk, with chronic hypertension posing a more significant threat than high blood pressure that develops later in pregnancy.
The Magnitude of Risk: From Data to Diagnosis
Investigators analyzed data from the CDC’s National Vital Statistics System, covering approximately 44 million live births in the U.S. from 2018 through 2024. Within this massive cohort, 27,764 infants were diagnosed with critical congenital heart disease (CCHD), a prevalence of 6.3 per 10,000 births. The study meticulously categorized maternal hypertensive disorders to pinpoint specific associations.
Mothers with chronic hypertension—defined as high blood pressure existing before pregnancy or diagnosed before 20 weeks—had a 30% higher adjusted odds of giving birth to an infant with CCHD. This translates to a predicted risk of 8.2 per 10,000 births, compared to 6.3 per 10,000 births for mothers without the condition. The link was strongest for this specific category of hypertension. In contrast, gestational hypertension (high blood pressure diagnosed after 20 weeks) showed only a borderline association, and eclampsia was not significantly linked to an increased risk of CCHD.
The prevalence of hypertensive disorders of pregnancy rose significantly during the study period, climbing from 9.4% in 2018 to 13.9% in 2024. This increase was driven primarily by a rise in chronic hypertension, suggesting a growing challenge for maternal-fetal health in the U.S.
Managing Blood Pressure Lowers Risk
- The risk of a baby having a serious heart defect is low overall, but it is about 30% higher for mothers with high blood pressure that starts before or early in pregnancy.
- High blood pressure that develops later in pregnancy (after 20 weeks) or the severe complication eclampsia does not appear to carry the same level of risk for these specific heart defects.
- Managing blood pressure before and during pregnancy is a key actionable step for women to potentially lower this risk.
Beyond the Numbers: Mechanisms and Medical Context
While the study establishes a strong association, it does not prove a direct cause-and-effect relationship. The “mechanism of action”—the biological pathway by which maternal high blood pressure might affect fetal heart development—remains an area of active investigation. The study itself identifies this as a key question for future research.
Study author Dr. Rahman noted that the findings “suggest that maternal heart health before and during pregnancy may have a particularly important relationship with fetal heart development.” He added that future studies should explore the biological mechanisms linking maternal hypertension and CCHD, and examine whether the risk is influenced by the timing, severity, and treatment of the hypertension during pregnancy.
Dr. Flora Nuñez Gallegos, a pediatric cardiologist at the University of California, San Francisco who was not involved in the research, echoed this sentiment. She emphasized that while the absolute risk remains low, the findings “highlight the importance of identifying and managing chronic hypertension before and during pregnancy.” She stressed that “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.”
Bridging Global Health Systems: A Call for Preconception Care
The implications of this research extend beyond the U.S. healthcare system, offering a valuable case study for global public health efforts. The study's reliance on birth certificate data shows the importance of accurate, comprehensive health record-keeping.
The findings align with the emphasis placed by the American Heart Association and the U.S. Centers for Disease Control and Prevention (CDC) on preconception care. The study provides solid data to support these existing guidelines and gives them renewed urgency.
As the study’s lead researcher stated, the research “underscores the critical need for early interventions and a proactive approach in managing chronic conditions before pregnancy.” This points to a need for healthcare systems worldwide to invest in resources and educational programs that facilitate better preconception counseling and care, potentially reducing the incidence of severe birth defects.
| Maternal Condition | Associated Risk of CCHD | Key Statistic |
|---|---|---|
| Chronic Hypertension | 30% Higher | 8.2 per 10,000 births |
| Gestational Hypertension | Borderline Increase | Odds Ratio: 1.08 |
| Diabetes (Type 1 or 2) | 48% Higher | Reported by Medical Daily |
| Eclampsia | No Significant Association | Not linked to CCHD |
Understanding the Data: Strengths and Limitations
The study’s great strength is its enormous scale. Analyzing 44 million births provides substantial statistical power to detect associations, even for relatively rare outcomes like CCHD. However, the study’s design as an observational analysis using birth certificate data also presents significant limitations that the authors acknowledge.
Birth certificates, while valuable, do not capture a wealth of clinically relevant information. The data lacks details on genetic factors, a mother’s full health history, the specific timing of hypertension diagnosis, the type and dosage of antihypertensive medications used, and crucially, how well blood pressure was controlled during pregnancy. As the American Heart Association noted, these omissions mean the study can only point to a link, not a definitive cause. The authors also highlight that the abstract has not been peer-reviewed, and the findings are therefore considered preliminary.
“The study does not show that one trend drove the other,” Medical Daily clarified, summarizing the core limitation. Because critical heart defects are rare, even a 48% higher relative risk still means the vast majority of babies born to mothers with diabetes or hypertension will not have one. The attributable risk— the proportion of CCHD cases linked to maternal chronic or gestational hypertension—was estimated to be approximately 1.5%.
Consult Doctors Before Pregnancy
This research highlights the importance of managing pre-existing health conditions for women planning a pregnancy. It is not a treatment recommendation but a call for proactive medical consultation. Women with chronic hypertension or diabetes should not stop or change their medications on their own, as some adjustments require medical supervision. The key is to work with a healthcare provider before conceiving to optimize health.
Signs in a newborn that warrant urgent medical evaluation include bluish skin or lips (cyanosis), trouble breathing, poor feeding, or unusual sleepiness. These symptoms could indicate a congenital heart defect and require immediate attention. All 50 U.S. states and Washington, D.C. screen newborns for critical heart defects using pulse oximetry, though a baby who passes the screen can still have a defect.
What’s Next? The Future of Maternal-Fetal Cardiology
This research serves as a powerful catalyst for future scientific inquiry. Dr. Rahman and his team have laid the groundwork, but the next steps are clear: to move from statistical association to biological understanding. Future research must examine the precise mechanisms by which maternal hypertension disrupts the intricate process of fetal heart development.
On a clinical front, the findings reinforce the standard of care but add a new layer of urgency. Preconception counseling for women with hypertension or diabetes is not just a recommendation; it is a critical intervention with the potential to significantly lower the incidence of severe, life-altering birth defects.
Frequently Asked Questions
What is the absolute risk of a heart defect for a mother with chronic hypertension? The study found a predicted risk of 8.2 per 10,000 births for mothers with chronic hypertension, compared to 6.3 per 10,000 for the general population.
Does this study prove that hypertension causes heart defects? No. The study is an observational analysis showing a strong association. It cannot prove causation due to limitations like the lack of data on blood pressure control and genetic factors.
Can controlling blood pressure lower this risk? While the study doesn’t provide direct evidence on this point, managing chronic conditions like hypertension before and during pregnancy is a key recommendation from experts like the CDC and Dr. Nuñez Gallegos to mitigate risks.
References
- Rahman SU, Shaukat MT, Rahman WU, et al. Maternal hypertensive disorders and critical congenital heart disease: a national cohort study of 44 million U.S. live births. Presented at: American Heart Association Scientific Sessions 2026; November 6-9, 2026; Chicago, IL. Abstract MDP1783.
- American Heart Association. Hypertension or diabetes before pregnancy linked to higher risk of fetal heart defects. Published November 2, 2026. Accessed November 7, 2026. https://newsroom.heart.org/news/hypertension-or-diabetes-before-pregnancy-linked-to-higher-risk-of-fetal-heart-defects
- CDC. Key Findings: Diabetes and Pregnancy.
