A study of hundreds of thousands of infants in France did not find any increased risk of birth defects among those whose mothers received a Covid vaccine in the first trimester, building on previous evidence for the vaccines’ safety.
The study — among the largest assessments to date of the safety of Covid vaccination in early pregnancy — comes as the Trump administration casts doubt on the safety and effectiveness of Covid vaccines for pregnant women, issuing conflicting messages and guidance that have left both patients and providers confused.
Published Wednesday in JAMA Network Open, the study looked at live births recorded in France’s national registry from pregnancies that began between April 2021 and January 2022. In total, health records were analyzed for nearly 530,000 infants — about 130,000, or roughly 25 percent, of whom were exposed to an mRNA Covid vaccine during the first trimester. It did not examine vaccination in the second or third trimester.
The researchers tracked the children’s health through December 2024 and found no indication that those whose mothers had received an mRNA Covid vaccine during the first trimester were at greater risk of any of dozens of birth defects — including various heart and digestive tract malformations, nervous system problems, chromosomal abnormalities, cleft palate and more — compared with children whose mothers hadn’t received a vaccine.
“This piece of evidence fits within the broader scope of the evidence that these vaccines are safe during pregnancy, and that the risk-benefit profile favors vaccination during pregnancy,” said Dr. Aaron Richterman, an assistant professor of medicine at the University of Pennsylvania who was not involved in the study.
The findings, the researchers wrote, provide “substantial reassurance that mRNA Covid-19 vaccines are highly unlikely” to lead to birth defects. The first trimester is a key period for organ development, and many factors during that period, including illnesses and certain medications, can interfere with that development — though risk also exists later in pregnancy.
Dr. Mahmoud Zureik, an author of the study, said that the results supported making Covid vaccines “widely available to all women who wish to be vaccinated during pregnancy.”
At least two previous large-scale studies — one in Canada and one in Denmark, Norway and Sweden — also did not find increased risk for congenital abnormalities associated with Covid shots in the first trimester. But those studies weren’t as large as the new one; they each involved fewer than 35,000 infants whose mothers were vaccinated during the first trimester, so they could have failed to identify associations with very rare birth defects. They also looked only at abnormalities grouped by body system (for example, heart defects), not at individual abnormalities (such as specific heart defects like pulmonary valve stenosis). The new study looked at both.
Dr. Richterman, who was part of a team that reviewed recent vaccine data for the University of Minnesota’s Vaccine Integrity Project, which was created this year to offer science-based advice on immunizations, called it “a very high-quality study.”
He said the large sample size had allowed the researchers to provide a more precise analysis than was previously available. For example, like previous studies, this one did not find an increased risk for cardiac malformations, but it went further and also didn’t find increased risk for any of 21 specific cardiac malformations.
The researchers did not examine vaccination after the first trimester, or look at whether the shots were associated with adverse pregnancy outcomes other than birth defects. But vaccination has been associated with a lower risk of outcomes like stillbirth, since Covid infections can hurt fetuses, and past studies have not found any increased risk of miscarriage. The shots also help protect pregnant women, who are at increased risk of severe illness from Covid.
Under Health Secretary Robert F. Kennedy Jr., public health agencies in the United States have issued muddled guidance on who should receive the latest Covid vaccines. The Centers for Disease Control and Prevention acknowledges that pregnancy is a high-risk condition — one of the criteria in the Food and Drug Administration’s limited approval of the shots — but in May stopped recommending Covid vaccination for pregnant women who were otherwise healthy.
This month, the agency revised its guidance to say pregnant women should consult with a medical provider before getting a vaccine.
That aligns with new federal guidance — more limited than in past years — saying that all Americans 6 months and older can get the shot after consulting a provider.
Maggie Astor covers the intersection of health and politics for The Times.
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