New evidence supports recommendations by health officials to get vaccinated against COVID-19 during pregnancy, with researchers finding that the shot is not associated with an increased risk of two adverse birth outcomes.
An analysis published Tuesday by the Centers for Disease Control and Prevention found COVID-19 vaccination during pregnancy was not associated with a higher risk of preterm birth – defined as giving birth before 37 weeks’ gestation – nor with smaller-than-usual babies when compared against births among unvaccinated women.
Researchers examined data from more than 40,000 women ages 16 to 49 who became pregnant in 2020 and gave birth in California, Colorado, Minnesota, Oregon, Washington and Wisconsin. Among that group, about 10,000 women received at least one COVID-19 vaccine dose between Dec. 15, 2020 and July 22, 2021.The vast majority received either the Pfizer or Moderna mRNA vaccines, while about 4% received the Johnson & Johnson vaccine.
Overall, the rate of preterm birth among all the women was 6.6 events for every 100 live births. Among pregnant women who had received any type of COVID vaccine, the rate of preterm birth was 4.9 for every 100 live births, compared with 7 per 100 among unvaccinated women.
The rate of babies who were born small-for-gestational age at birth – defined as having a birthweight below the 10th percentile for their gestational age – remained constant at 8.2 per 100 live births among pregnant women overall and among both vaccinated and unvaccinated pregnant women.
Researchers also assessed rates for both outcomes based on how many doses of the Moderna or Pfizer vaccines a woman had received and whether they’d received their first or only vaccine dose in either the second or third trimester. Though rates fluctuated, they still found no significant association between the shot and a higher risk of the two outcomes.
The study’s findings support CDC recommendations for pregnant people to get vaccinated due to an increased risk of severe illness tied to COVID-19 compared with people who are not pregnant, even as the agency says the overall risks are low. People who are pregnant and have COVID-19 face increased risks of preterm birth and stillbirth, according to the CDC.
Researchers in the CDC-published study acknowledged, however, that the timing in which the COVID-19 vaccine became available and the timing of births among women in their cohort may have contributed to the fact that only 1.7% of women who got vaccinated did so during their first trimester.
“Risks associated with vaccination during the first trimester should be evaluated in future studies that include vaccines administered throughout pregnancy,” the study says.
The findings of the new study may help dispel concerns over vaccine safety among a group that’s had a low vaccination rate despite increased risks. Overall, only about 22% of the more than 40,000 women in the study had received at least one dose of a COVID-19 vaccine between mid-December of 2020 and late July of the next year. In late September of last year, CDC Director Dr. Rochelle Walensky said only about 30% of women currently pregnant had been vaccinated.
“The findings from this retrospective, multisite cohort of a large and diverse population with comprehensive data on vaccination, comorbidities, and birth outcomes add to the evidence supporting the safety of COVID-19 vaccination during pregnancy,” the study authors concluded.