(HealthDay)—A new study suggests the rate of COVID-19 among pregnant women without symptoms is much lower than previously reported.

Fewer than 3% of asymptomatic women admitted to three Yale New Haven Health hospitals for labor and delivery during April tested positive for COVID-19 infection.

That contrasts with a 13.5% rate reported in a study of asymptomatic pregnant women admitted to hospitals in New York City, an epicenter of the U.S. outbreak.

The new study included 770 hospital patients who hadn't previously been diagnosed with coronavirus infection. Of those, 30 tested positive for COVID-19. Of those who tested positive, 22 had no symptoms—meaning the rate of positive tests among asymptomatic women was 2.9%.

No patients who tested negative for COVID-19 developed symptoms or required further testing, and no health care workers on the obstetric units had to stop work due to COVID-19 illness or exposure from a known or possible contact with a patient, the findings showed.

While the number of asymptomatic women who tested positive rose 10-fold during the study, the number with symptoms declined by half, the researchers said.

The study was published as a letter in the May 24 issue of the Journal of the American Medical Association.

"Our report provides reassuring information on infection rates and appropriate hospital responses outside of highly endemic areas," said corresponding author Dr. Katherine Campbell. She's medical director of Yale New Haven Hospital's Labor and Birth and Maternal Special Care Units.

"Not only have we provided insight into the nature of a positive test, we've highlighted how a comprehensive testing program can reduce the use of personal protective equipment among labor and delivery staff without increasing their risk of exposure," Campbell said in a news release.

Among people who have recovered from COVID-19, tests can yield positive results for up to six weeks, noted study co-author Dr. Christian Pettker, chief of obstetrics at Yale New Haven Hospital.

"Given our data, we think that a large number of the asymptomatic patients who test positive might not actually be actively infected or infectious," he said in the news release. "This requires more research but has very important implications for patients who test positive who then might have to be isolated and separated from their babies."

For patients, this might be even more noteworthy than the fact that labor units are much safer than has been reported, he added.

More information: The U.S. Centers for Disease Control and Prevention has COVID-19 advice for women who are pregnant or breastfeeding.

Journal information: Journal of the American Medical Association 

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