CNN
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Pregnant women and their developing babies are at higher risk for severe outcomes if they get Covid-19, and now a large, international review is helping to underscore how devastating those risks can be.

The study draws on data from 12 studies from as many countries—including the United States. Altogether, the studies included more than 13,000 pregnant women—about 2,000 who had a confirmed or probable case of Covid-19. The health outcomes for these women and their babies were compared to about 11,000 pregnancies where the mother tested negative for Covid-19 or antibodies to it at the time of their deliveries.

Across the studies about 3% of pregnant women with Covid-19 needed intensive care, and about 4% needed any kind of critical care, but this was far higher than the numbers of pregnant women who needed that kind of care outside of a Covid-19 infection.

Compared to pregnant individuals who weren’t infected, those who got Covid-19 were nearly 4 times more likely to be admitted to an intensive care unit. They were 15 times more likely to be ventilated and were 7 times more likely to die. They also had higher risks for pre-eclampisa, blood clots, and problems caused by high blood pressure. Babies born to moms who had Covid-19 were at higher risk for preterm birth and low birth weights.

Previous studies have suggested that Covid-19 may increase the risk of stillbirth, but this study didn’t find that same link.

Still, the findings paint a clear picture that shows the risks of pregnancy are amplified by Covid-19 infections.

“It’s very clear and even it’s consistent, you know, whether we’re talking about Sweden where we have really generally great pregnancy outcomes to other countries that you know, have bigger problems with maternal morbidity and mortality, that having COVID and pregnancy increases risk for both mom and baby,” said lead study author Emily Smith, who is an assistant professor of global health at George Washington University.

The study has some caveats that may limit how applicable the findings are to pregnant individuals in the Omicron era.

First, the studies were conducted relatively early in the pandemic, at a time when most people were still unvaccinated and uninfected. That means people in the study were likely at higher risk not just because they were pregnant, but also because they were immunologically naïve to the virus—they didn’t have any pre-existing immunity to help them fight off their infections.

Since then, many pregnant individuals have gotten vaccinated, or had Covid-19 or both. As of the first week of January, about 72% of pregnant people in the U.S. have had their primary series of Covid-19 vaccines, and about 95% of Americans are estimated to have had Covid-19 at least once, or been vaccinated against it, according to data from the Centers for Disease Control and Prevention. That means it’s likely they have some immune memory against the virus that may help protect against severe outcomes.

That immune memory appears to fade over time, however. CDC data show just 19% of pregnant women have had an updated booster, meaning many people may not have as much protection against the virus as they think they do.

Lead study author Emily Smith, who is an assistant professor of global health at George Washington University, says the study results reflect the risk of Covid-19 and pregnancy in unvaccinated people.

Unfortunately, Smith says, many countries still don’t have clear guidelines advising vaccination during pregnancy. And there are some parts of the world, such as China, that still have substantial proportions of their population who’ve never been been infected.

For people who are trying to weigh the risks and benefits of Covid-19 vaccination during pregnancy, Smith says this study helps tip the scales firmly on the side of vaccination.

“It’s worth it to protect yourself in pregnancy,” Smith said.

She says this study didn’t look at the benefits of vaccination in pregnancy, but other studies have, showing big decreases in the risk of stillbirth, preterm birth and severe disease or death for mom.

“And so that’s kind of the complementary story,” said Smith.

Dr. Justin Lappen, division director of Maternal Fetal Medicine at the Cleveland Clinic, praised the study and said its findings reinforce and advance previous research, which has found that Covid-19 markedly increases the risk of severe outcomes for mom and baby. He wasn’t involved in the study.

He says the findings highlight the importance of preventing and treating Covid-19 in pregnant women.

Therapies that are indicated or otherwise recommended should not be withheld specifically due to pregnancy or breastfeeding, Lappen wrote in an email to CNN.

The study is published in the journal BMJ Global Health.