Receiving a COVID-19 vaccine early in pregnancy is not associated with an increased risk for spontaneous abortion, new research suggests.

The study, published online in JAMA looked at the proportion of women who received the vaccine and had ongoing pregnancies in comparison with those who experienced a miscarriage or spontaneous abortion.

The researchers analyzed data from 105,446 unique pregnancies over seven 4-week surveillance periods between December 2020 and June 2021. Ongoing pregnancies between 6- and 19-weeks’ gestation were identified on the last day of each 4-week surveillance period (index date). Spontaneous abortions were assigned to a 4-week surveillance period on the basis their outcome date. There were 13,160 spontaneous abortions and 92,286 ongoing pregnancies.

Overall, a COVID-19 vaccine was received within 28 days prior to an index date among 8.0% of ongoing pregnancy surveillance periods vs 8.6% of spontaneous abortions.

"We're hoping that this data can inform the ongoing conversations between providers and pregnant women [about the COVID-19 vaccines]," study author Elyse O. Kharbanda, MD,

senior research investigator at HealthPartners Institute, tells Medscape Medical News.

"It should be considered in the context of all the data that's coming out both on the risks of COVID infection and pregnancy and data on outcomes among women who are vaccinated and pregnant."

Among the women whose pregnancies were followed, 7.8% received at least one dose of the Pfizer COVID-19 vaccine, 6% received at least one dose of the Moderna COVID-19 vaccine, and 0.5% received the Johnson & Johnson vaccine.

In August, the American College of Obstetricians and Gynecologists (ACOG), the CDC , and the Society for Maternal-Fetal Medicine strongly recommended that all pregnant women be vaccinated against COVID-19.

The new findings provide reassuring evidence about the safety of COVID vaccines, particularly mRNA vaccines, during pregnancy, says Denise J. Jamieson, MD, chair of the Department of Gynecology and Obstetrics at Emory University School of Medicine, Atlanta, Georgia, who was not involved in the study.

"The study design was a carefully conducted case-control study. Although ideally the best design for studying vaccine safety and efficacy is a randomized clinical trial, data are rapidly accumulating from a variety of sources that COVID vaccines are safe in pregnancy," says Jamieson, who serves on several ACOG committees.