Third-trimester Omicron infection linked with preterm birth - study

Infection with the Omicron variant of the coronavirus in the third trimester of pregnancy is linked with an increased risk of preterm delivery, according to Israeli researchers.

Doctors there compared 2,753 pregnant patients with positive PCR tests for the virus this year to the same number of similar but uninfected pregnant patients. Infections were not associated with preterm birth when diagnosed in the first or second trimester.

But nearly half of the women were infected in the third trimester.

In this group, rates of preterm birth were 5.8%, compared to 2.3% among uninfected women at the same stage of pregnancy, the study found.

After accounting for other risk factors, women diagnosed in the third trimester were nearly three times more likely than uninfected women to delivery early, and those diagnosed after 34 weeks of gestation were roughly seven times more likely to have late preterm births, according to a report published on Wednesday in the journal PLOS One.

Symptomatic infections increased the risks even further.

"Women during their third trimester, specifically after 34 weeks of gestation, should practice social distancing and respiratory protection to reduce risk of adverse pregnancy outcomes," the researchers wrote.

They added that women at earlier stages of pregnancy should not let down their guard because the study did not evaluate "other potential differences in the mother or newborn." -- Reuters