COVID-19 vaccination during pregnancy not linked to complications at birth: U.S. study

COVID-19 vaccination during pregnancy was not associated with preterm delivery or underweight newborns, according to a study published by the U.S. Centers for Disease Control and Prevention (CDC) on Tuesday.

The rate of preterm birth was roughly five per cent among more than 10,000 women who received at least one dose of a COVID-19 vaccine, compared to seven per cent for roughly 36,000 unvaccinated women, researchers said on Tuesday in the CDC's Morbidity and Mortality Weekly Report. The difference was not deemed to be statistically significant.

In addition, COVID-19 vaccination did not increase the risk of delivering a baby who weighed less than usual for the number of weeks of pregnancy, the researchers found.

Results from the study support the CDC's recommendation on the safety of COVID-19 vaccination during pregnancy, and echo the advice of numerous Canadian physicians who have long recommended pregnant individuals get vaccinated given the high risks associated with a coronavirus infection during pregnancy.

"Pregnancy is a time where we all want to be careful with what we're doing to our body, but the data shows the benefits outweigh any potential side effects of the vaccine during pregnancy," Dr. Jesse Papenburg, a pediatric infectious disease specialist at the Montreal Children's Hospital, said on Tuesday.

As CBC News previously reported, data compiled by the Canadian Surveillance of COVID-19 in Pregnancy team showed women who are pregnant are nearly five times more likely to be admitted to hospital for COVID-19 than their non-pregnant peers — and 10 times more likely to be admitted to an intensive care unit.

"Evidence of the benefits of COVID-19 vaccination during pregnancy continues to accrue, including the detection of antibodies in cord blood," the CDC researchers wrote, also noting that pregnant women with COVID-19 have increased risks of ICU admission, need for mechanical ventilation and death.

The women in the study had become pregnant between May and October 2020, before vaccines were available.

Nearly all who were vaccinated got the shots in their second or third trimester. Some 96 per cent of them had received at least one dose of an mRNA vaccine from either Pfizer and BioNTech or Moderna. The remaining women received the single-shot vaccine from Johnson & Johnson.

The data was drawn from eight health-care organizations in six U.S. states, the report said.

The researchers noted that because they reviewed data collected for other purposes, they may have missed some vaccinations, and they lacked information on women's previous history of birth-related complications. The study also lacked information on first-trimester vaccinations and on boosters, which were not available at the time.