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Getting an mRNA COVID-19 shot during the first trimester of pregnancy didn't lead to an increased risk of major structural birth defects, a multisite retrospective cohort study found.

Major structural birth defects occurred in 1.48% of infants after a first-trimester vaccination and in 1.41% of those without a first-trimester vaccination (adjusted prevalence ratio 1.02, 95% CI 0.78-1.33), Elyse Kharbanda, MD, MPH, of the HealthPartners Institute in Bloomington, Minnesota, and colleagues reported .

Additionally, secondary analyses revealed that there were no significant differences between groups when birth defects were grouped by organ system.

"These findings should provide reassurance to pregnant people and their obstetric care practitioners," the authors concluded.

Kharbanda described the research as "a big data study" using data across Vaccine Safety Datalink sites, which have robust data on COVID-19 vaccine exposure and algorithms that identify pregnancies, link moms and babies, and identify birth defects.

"Other vaccines are administered in [the] first trimester and we've never had a safety concern related to first-trimester vaccines and birth defects," Kharbanda told 番茄社区app. "But it's part of our purview and responsibility to study these outcomes and it's something that pregnant people worry about, so it's something that it's always good to have data to confirm."

It's already been well established that getting COVID during pregnancy increases the risk of pregnancy complications and adverse birth outcomes, the authors noted. The American College of Obstetricians and Gynecologists recommends that pregnant people get vaccinated against COVID .

The study adds to the growing body of research supporting the safety of COVID vaccination for pregnant people and their babies, including that the vaccine is safe for infant brain development and lowers the risk of adverse neonatal outcomes.

Pamela Berens, MD, an ob/gyn at the McGovern Medical School at UTHealth Houston, said that she was happy to have a large study that further demonstrated mRNA COVID vaccine safety for pregnant patients, though she wasn't surprised by these results.

"I think that this should be reassuring to people who continue to have concerns about the safety of this vaccine in pregnancy," Berens said.

Cardiac defects were by far the most prevalent birth defect in both groups, seen at a rate of 68.1 and 60 per 10,000 live births for the first-trimester vaccinated and unvaccinated groups, respectively, which was not a significant difference, the researchers reported.

Neural tube (5.2 and 2 per 10,000, respectively) and gastrointestinal (23.6 and 20 per 10,000, respectively) defects were slightly, but not significantly, more prevalent in the first-trimester group, while kidney and genitourinary defects were less prevalent in the first-trimester group (28.8 and 39.1 per 10,000, respectively).

This retrospective cohort study used data from eight health systems in California, Oregon, Washington, Colorado, Minnesota, and Wisconsin and compared women who had one or two mRNA COVID-19 vaccines in their first trimester with pregnant women who were either unvaccinated or vaccinated at a different time. Participants had singleton pregnancies with a live birth between March 5, 2021 and Jan. 25, 2022.

On average, people vaccinated in the first trimester skewed older, with a mean maternal age of 32.3 compared with 30.6 in the control group. In total, 18.1% of eligible pregnancies (7,632 of 42,156) received an mRNA COVID-19 vaccine in the first trimester.

The majority of those not vaccinated in the first trimester were unvaccinated both before and after pregnancy (55%), while 5.9% were vaccinated before pregnancy and 39.1% during the second or third trimester. After applying stabilized inverse probability weighting, there were negligible differences in baseline characteristics between groups, the researchers said.

The authors noted several limitations, including that data were only available for pregnancies ending in live birth, which eliminated more severe birth defects that resulted in stillbirth. They also didn't have data on folic acid use, and only birth defects diagnosed by 4 months of age were able to be evaluated. Lastly, they only analyzed mRNA COVID-19 vaccines.

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