Pre-pregnancy blood pressure and diabetes track with higher fetal heart defect risk
Maternal cardiovascular health before conception appears to matter far earlier than delivery, and this analysis of more than 44 million U.S. births draws a direct line between chronic hypertension, pre-pregnancy diabetes, and critical congenital heart disease in infants. Women with chronic hypertension before pregnancy or diagnosed before 20 weeks were associated with a 30% higher risk of delivering a baby with critical congenital heart disease compared with women whose blood pressure stayed normal before and during pregnancy. Women with Type 1 or Type 2 diabetes before pregnancy carried a 48% higher risk.
The finding is clinically stark because critical congenital heart disease is not a subtle phenotype. It is the most severe form of congenital heart disease, often requiring surgery or catheter-based intervention in the first year of life and ongoing specialty follow-up after that. In practical terms, the fetal heart is developing in an environment shaped by maternal vascular status, glucose metabolism, placental perfusion, and inflammatory signaling. When those systems are disrupted before conception, the embryo may be exposed during the narrow window when cardiac structures are forming.
One sentence captures the bedside consequence: preconception control of blood pressure and diabetes is not just maternal risk reduction; it is fetal cardiac risk reduction.
Chronic hypertension carried the strongest signal in the 44 million-birth cohort
The analysis used National Vital Statistics System natality data from 2018 through 2024 and included more than 44 million live births in the United States. Nearly 28,000 infants, or 0.06%, were diagnosed with critical congenital heart disease during that period. About 1.5% of those cases were linked to chronic or gestational hypertension.
Across the study years, maternal hypertension became more common. Prevalence rose nearly 48%, from about 9.4% of pregnancies in 2018 to 13.9% in 2024. Critical congenital heart disease also increased, from 5.8 cases per 10,000 births in 2018 to 6.4 cases per 10,000 births in 2023-2024. That translated to nearly 4,000 affected infants in the U.S. each year.
The association was not uniform across hypertensive disorders. Chronic hypertension showed the clearest relationship with infant risk, while gestational hypertension was linked to a smaller increase of 8% in the likelihood of critical congenital heart disease. Eclampsia was not significantly associated with the outcome. Chronic plus gestational hypertension fell within the study’s blood pressure categories, but the most clinically compelling signal came from hypertension already present before pregnancy or identified early enough to qualify as chronic.
The pattern fits biologic plausibility. Long-standing hypertension can affect maternal vasculature and placental development before organogenesis is complete, potentially altering oxygen and nutrient delivery during the period when the heart’s structure is being laid down. Diabetes adds a second layer of risk through hyperglycemia, which can disrupt embryologic development and has long been tied to congenital malformations, including those of the heart.
Why the timing of maternal disease matters for fetal heart development
The investigators adjusted for several maternal factors, including demographics, Type 1 or Type 2 diabetes, smoking status, pregnancy history, and pregnancy length. Even with those adjustments, the association between chronic hypertension and critical congenital heart disease remained. The absolute risk stayed low, but low absolute risk does not erase the burden for families or the need for prevention in high-risk pregnancies.
Flora Nuñez Gallegos, a pediatric cardiologist at the 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, framed the result in a way clinicians will recognize immediately: the strongest association was seen with chronic hypertension, not gestational hypertension, which points back to maternal health before pregnancy begins. That distinction aligns with fetal cardiac biology. By the time gestational hypertension appears after 20 weeks, much of cardiac morphogenesis has already taken place.
The study also raises a familiar public health concern. Hypertension affects about 16% of pregnancies, according to the 2025 American Heart Association/American College of Cardiology guideline cited in the release. If the prevalence of hypertensive disorders is rising during pregnancy, the pool of pregnancies exposed to elevated vascular risk before organ development is complete grows with it.
What birth-certificate data can and cannot answer
This was an observational analysis, so the findings identify associations rather than prove direct causation. The design cannot determine whether treating blood pressure before or during pregnancy reduces the risk of critical congenital heart disease. It also cannot separate the influence of individual antihypertensive medications, blood pressure severity, or how tightly blood pressure was controlled.
Several important variables were unavailable in the birth-certificate data. The analysis did not capture genetic factors, maternal health history beyond what is recorded in the file, prenatal imaging, the timing of high blood pressure during pregnancy, whether treatment was received, or how consistently treatment was taken over time. Those gaps matter because the fetal heart is shaped by more than one physiologic pathway, and birth-certificate surveillance cannot fully reconstruct the maternal-fetal environment.
Still, the scale of the dataset gives this abstract unusual weight. More than 44 million births offer enough statistical breadth to detect signals that smaller cohorts may miss. The result is not a final answer, but it is a clinically meaningful warning light.
Rahman said future studies should examine the biologic mechanisms linking maternal hypertension and critical congenital heart disease, along with the role of timing, severity, and treatment during pregnancy. Those are the right questions, because the next step is not simply to count defects more precisely. It is to determine whether earlier blood pressure diagnosis, tighter control before conception, and aggressive management of diabetes can alter fetal cardiac outcomes in a measurable way.
The abstract remains preliminary until full peer-reviewed publication. Even so, the message for obstetric, primary care, and cardiology teams is already concrete: blood pressure and glucose control before pregnancy may influence not only maternal outcomes, but also whether a fetus develops the most severe forms of heart disease.