A study of more than 40,000 pregnant women finds no increased risk of preterm or small-for-gestational-age births among babies delivered by women who received COVID-19 vaccines.

The report, which includes data from Bloomington-based HealthPartners, follows a September study from the same research group that found pregnant women vaccinated against COVID-19 did not see an increased risk of miscarriages.

The findings should be reassuring to pregnant women, particularly as the spread of the highly contagious omicron variant makes it harder for expectant mothers to avoid the virus through means other than vaccination, said Dr. Elyse Kharbanda, senior author on the study and executive director of research with HealthPartners Institute.

"Pre-omicron, you'd talk about, well, if you can control your risks — maybe you don't have other children at home, you're working from home — that you can be careful and control your risks," Kharbanda said Tuesday. "I think now with this highly contagious variant, I don't know — controlling your risks seems a little bit harder and I think vaccination is the best way to prevent real complications and morbidity due to infection."

The report uses information from the Vaccine Safety Datalink, a collaborative of independent researchers that's backed by the Centers for Disease Control and Prevention (CDC) to look for safety issues with vaccines across patients treated at large medical centers in six states. HealthPartners is one of the medical groups that participates in the research effort.

The new report, which is being published in CDC's Morbidity and Mortality Weekly report, looked at birth outcomes among 46,079 pregnant women who were expected to deliver babies between February and July 2021. Just over 10,000 pregnant women in the group received at least one vaccine dose.

Preterm birth is when a baby is born before the 37th week of pregnancy. Babies are considering small for gestational age (SGA) when weight at birth is below the 10th percentile for gestational age.

"In this large, multisite, retrospective cohort study, receipt of COVID-19 vaccine during pregnancy was not associated with increased risk for preterm birth or SGA at birth," the study concludes.

"The absolute risk for severe morbidity associated with COVID-19 in pregnancy is low; however, women with symptomatic COVID-19 during pregnancy have a more than two-fold increased risk for intensive care unit admission, invasive ventilation, and extracorporeal membrane oxygenation, and a 70% increased risk for death, compared with nonpregnant women with symptomatic infections."

To reduce COVID-19 risks, CDC recommends vaccination for women who are pregnant and recently pregnant (including those who are breastfeeding). The recommendation also applies to women who are trying to become pregnant now, or who might become pregnant in the future.

"Many unvaccinated people who are pregnant have concerns about the vaccines, and some skepticism is understandable. But, getting infected with COVID-19 during pregnancy can result in severe disease," Kharbanda said in a statement. "We now have the data to show that COVID-19 vaccines are safe for pregnant people, and COVID-19 infection is really unsafe for pregnant people. So, it's important to consider vaccination if you're pregnant."