Pregnant women who catch COVID infection are at an increased risk of developing severe illness, and yet only 30% of pregnant women in the United States had received vaccines as of Sep. 2021.

Most pregnant women are hesitant to take the vaccine because they think vaccines might disrupt pregnancy.

However, a Yale co-led study has added new evidence supporting the safety of COVID-19 vaccination during pregnancy. The study, reported by the Centers for Disease Control and Prevention (CDC), looked at more than 40,000 pregnant women.

Researchers found that vaccination during pregnancy was not linked to preterm birth or small-for-gestational-age (SGA). They also found that the trimester when the vaccination was received and the number of vaccine doses received were also not associated with increased risk of preterm birth or SGA, according to Medical Xpress.

Also called premature birth, preterm birth is the birth of a baby at fewer than 37 weeks gestational age, while in SGA, babies are delivered smaller in size than normal for the gestational age. Both preterm and SGA have been associated with a greater risk for infant death and disability.

Among those 40,000 pregnant individuals, more than 10,000 (22%) received at least one COVID-19 vaccine dose during pregnancy, according to the researchers said. More than 98% received vaccination during their second or third trimester and the rest received it during their first trimester of pregnancy. Around 96% of those vaccinated received either Pfizer-BioNTech or Moderna vaccine.

The researchers said the new findings add to the evidence that COVID vaccination is safe during pregnancy.

Experts believe that a lack of information about vaccine safety and potential harm to the fetus have been the drivers behind vaccine hesitancy among pregnant women.

Lead author Dr. Heather Lipkind said the results of this study speak to both of these drivers.

“Getting vaccinated against COVID-19 is important for preventing severe illness in pregnant people,” Dr. Lipkind said. “With the increasing rates of COVID-19 in our community, we are encouraging pregnant people to get vaccinated.”

In addition to having a risk of severe illness and even death, unvaccinated pregnant individuals are more likely to require admission into the ICU, mechanical ventilation, and machine-assisted blood oxygenation. Meanwhile, the CDC and the American College of Obstetricians and Gynecologists have been recommending COVID-19 vaccines for people who are pregnant, breastfeeding, and trying to get pregnant.