Unvaccinated pregnant women with COVID-19 are more likely to have poor delivery outcomes, even if they do not have severe respiratory difficulties during infection, according to a new study.

COVID-19 infection during pregnancy increased the risk of preterm birth, small for gestational age, low birth weight, and stillbirth.

Preterm birth and stillbirth were more common in women who were infected with SARS-CoV-2 during the first or second trimester, while increased rates of small for gestational age were mostly due to third trimester infection.

The electronic health records of almost 18,000 women who had SARS-CoV-2 tests during pregnancy were reviewed in a study led by the Institute for Systems Biology. Researchers compared the outcomes of 882 unvaccinated pregnant people who had a positive test to those who had a negative test.

“We found that SARS-CoV-2 infection indicated increased rates of preterm delivery and stillbirth, largely driven by first and second trimester infections,” says Samantha Piekos, first author of the study.

“The single greatest predictor of gestational age at delivery is gestational age at infection, with earlier age at infection associated with earlier age at delivery.”

The participants in the study had SARS-CoV-2 infections that were mild to moderate. The severity of maternal COVID-19 infection was not associated with the gestational age of the baby at delivery. Furthermore, even if maternal COVID-19 infection did not cause severe respiratory difficulties during infection, unfavorable birth outcomes were observed.

The findings are among the first to account for the impact of SARS-CoV-2 infection on birth outcomes, and were published today in the journal The Lancet Digital Health.

People in the SARS-CoV-2-positive group were more likely to be of Hispanic ethnicity, of a race other than Asian or White, to have Medicaid insurance, to be younger, to have a higher BMI, to have less education, and to have other variables linked to poor birth outcomes. In order to make a true apples-to-apples comparison, the researchers used a statistical matching method that took into account the things that might be influencing the results.

“Pregnant people are at an increased risk of adverse outcomes following SARS-CoV-2 infection, even when maternal COVID-19 is less severe, and they may benefit from increased monitoring following infection,” concludes Jennifer Hadlock, corresponding author of the paper and assistant professor at ISB. “Both maternal and fetal health are at increased risk with COVID-19. Therefore, this reinforces the importance of protecting pregnant women,” she added.

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