Study links COVID-19 vaccination in pregnancy to higher rates of hypertensive disorders

A new peer-reviewed study involving researchers from the Centers for Disease Control and Prevention (CDC) has reported a statistically significant increase in self-reported hypertensive disorders of pregnancy (HDP) among women who received a COVID-19 vaccine during or shortly before pregnancy, compared with unvaccinated women.

The study, published in the journal Vaccine, analyzed data from more than 16,000 first-time pregnancies and found that vaccinated women had a 24 percent higher risk of reporting hypertensive disorders such as gestational hypertension and preeclampsia.

These conditions are among the leading causes of maternal and fetal illness and death in the United States.

Researchers compared vaccinated women enrolled in the CDC’s COVID-19 Vaccine Pregnancy Registry with unvaccinated women drawn from the CDC’s Pregnancy Risk Assessment Monitoring System.

All participants were first-time mothers carrying single pregnancies, and women with known chronic hypertension were excluded from the analysis.

To reduce bias, the researchers matched participants one-to-one based on age, race, ethnicity and length of pregnancy at delivery. The analysis also adjusted for additional factors including body mass index (BMI), diabetes status, state of residence and year of delivery.

According to the findings: 15 percent of vaccinated women reported hypertensive disorders of pregnancy. 12 percent of unvaccinated women reported the same conditions.

After adjusting for potential confounding variables, vaccinated women remained significantly more likely to report HDP.

The increased risk was observed regardless of which COVID-19 vaccine the women received or the timing of vaccination during pregnancy.

The study also found that women who contracted COVID-19 during pregnancy had a 28 percent higher risk of hypertensive disorders compared to those who did not become infected. Researchers noted that the magnitude of risk associated with vaccination was similar to that associated with infection.

The authors emphasized that the findings do not establish a causal relationship between vaccination and hypertensive disorders. They cautioned that differences between the vaccinated and unvaccinated groups — including the fact that they were drawn from different surveillance systems and time periods — limit the ability to draw firm causal conclusions.

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They called for continued safety monitoring and updated risk-benefit analyses regarding COVID-19 vaccination during pregnancy.

The study relied on self-reported diagnoses, though validation analyses reportedly showed strong agreement between self-reported hypertension and medical records. Researchers acknowledged other limitations, including differences in job types and stress exposure.

Nearly half of the vaccinated participants were healthcare workers, a group that experienced heightened stress during the pandemic and may have had different health monitoring practices.

In April 2021, then-CDC Director Rochelle Walensky publicly encouraged pregnant women to receive COVID-19 vaccines, describing them as safe, even as the agency acknowledged that data on pregnancy safety were initially limited.

The American College of Obstetricians and Gynecologists (ACOG) continues to recommend COVID-19 vaccination during pregnancy. On its website, ACOG maintains that available evidence supports the safety of the vaccines for pregnant individuals.

However, some critics argue the new findings warrant deeper scrutiny. Epidemiologist Nicolas Hulscher said the results raise accountability questions, while other researchers note that safety monitoring systems are designed precisely to detect potential risks over time.

Possible Biological Mechanisms

The study authors discussed several biologically plausible mechanisms that might explain the association.

One involves the SARS-CoV-2 spike protein, which interacts with ACE2 receptors found on placental cells. These receptors play a role in blood pressure regulation.

Because mRNA vaccines prompt cells to produce the spike protein, some researchers have observed temporary increases in blood pressure following vaccination in non-pregnant populations.

Another potential mechanism is immune activation and inflammation triggered by vaccination. Inflammation early in pregnancy can affect placental blood flow and has been linked to hypertensive complications.

At the same time, COVID-19 infection itself has been associated with inflammation and vascular effects that could similarly increase the risk of hypertensive disorders.

The CDC’s present guidance on COVID-19 vaccination during pregnancy appears to be in transition. While the agency reportedly scaled back routine recommendations last year, its website currently lists “no guidance/not applicable” for COVID-19 vaccines in pregnancy.

The study concludes by urging renewed evaluation of pregnancy-related risks linked to both COVID-19 infection and vaccination, underscoring the need for transparent data and continuous monitoring to inform public health decisions.

Health experts stress that pregnant women should consult their healthcare providers to assess individual risks and benefits when making vaccination decisions.