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An international study suggests babies born to mothers who get Covid-19 during pregnancy are more likely to develop a breathing disorder.
The study by researchers at the University of California, Los Angeles found infants were three times as likely to have respiratory distress if their mothers were unvaccinated and had Covid-19 during pregnancy.
Neonatal respiratory distress (NRDS) is usually found in premature babies born more than six weeks before their due dates, but the study noted many babies developed NRDS later than anticipated.
One of the researchers, Professor Karin Nielsen said they carefully evaluated their data and found the respiratory distress was occurring not just in premature babies but also those who were born at term.
Nielsen said the researchers are continuing to follow these babies and looking for long-term effects such as whether the group is more susceptible to having asthma or other breathing problems when they get older.
Researchers found 17 percent of babies who had been exposed to Covid-19 during pregnancy developed NRDS shortly after birth, compared to the usual rate of 5 or 6 percent in the general population.
The authors studied 221 mothers, 151 of whom were unvaccinated.
Nielsen said they found babies whose mothers had been vaccinated before catching the virus were less likely to develop issues.
"When we did our analyses the mothers of babies who had been vaccinated during pregnancy before they got Covid, actually the frequency of respiratory distress was much lower in this group and the mothers who were unvaccinated had a three-fold higher chance of having a baby with respiratory distress."
It seemed there was a protective effect in preventing this from happening even if the mother had only had one dose of the vaccine, she said.
The researchers said exposure to Covid-19 in the womb sparked an "inflammatory cascade" that increased the risk of developing a breathing disorder.
Nielsen said Covid leads the pregnant women to have an inflammatory response.
"The babies are responding with their own inflammatory process when they are exposed to maternal inflammation, so this triggers in the baby what we call an inflammatory response and the respiratory distress is a symptom of this inflammatory response - they develop it shortly after birth."
Covid can create "a hostile in utero environment for the babies developing in the womb" because they are exposed to maternal inflammation, fever and inflammatory proteins, she said.
The authors acknowledged that the sample was limited, with most participants enrolling from a medical centre that received particularly severe patients.
The peer-reviewed study was published in the Nature Communications journal.
