Researchers in Scotland are urging pregnant women to get vaccinated after publishing a study that found that women who are infected with COVID-19 late in their pregnancies are more likely to experience serious complications, including the deaths of their babies.

The peer-reviewed study, published Thursday in the journal Nature Medicine, analyzed data from about 145,000 pregnancies in Scotland from Dec. 1, 2020, to Oct. 31, 2021. 

The scientists found alarming trends for women who were infected with the coronavirus 28 or fewer days before their delivery date. The rate of stillbirths and newborn deaths was 22.6 per 1,000 births — four times higher than in the general population. All of those deaths involved unvaccinated mothers, the study said.

Meanwhile, the rate of premature births was higher among mothers who had been infected with COVID-19 during the previous four weeks — 17% compared to 8% in the general population.

The researchers, however, stressed that it’s impossible to determine if COVID-19 contributed directly to the preterm births or deaths because they did not have access to detailed clinical records.

The study noted that the vaccination rate among pregnant women in Scotland is significantly lower than in the general population of women of similar age. Fewer than a third of women who gave birth in October were fully vaccinated, compared to 77% of women ages 18 to 44.

“Our data add to the evidence that vaccination in pregnancy does not increase the risk of complications in pregnancy, but Covid-19 does,” Dr. Sarah Stock, a maternal-fetal medicine specialist at the University of Edinburgh’s Usher Institute and the paper’s lead author, said in a news release. 

According to the study, just 11% of pregnant women who were infected with COVID-19 were fully vaccinated. Meanwhile, 91% of those who were hospitalized and 98% of those who required intensive care for the virus were unvaccinated. Unvaccinated pregnant women were four times as likely to be hospitalized as vaccinated women.

“It is clear that vaccination is the safest and most effective way for pregnant women to protect themselves and their babies from severe COVID-19 disease,” Dr. Rachael Wood, a consultant at Public Health Scotland and a co-author of the paper, said in a news release.

In the United States, where 73% of all adults are fully vaccinated, just 42% of pregnant women are inoculated, according to data from the Centers for Disease Control and Prevention. 

Early research has found no evidence that the Pfizer and Moderna mRNA vaccines cause any serious side effects in pregnant women, and the CDC recommends anyone who is pregnant, is breastfeeding or might become pregnant in the future to get vaccinated. 

Vaccines can be administered at any time during pregnancy.