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Researchers found the coronavirus and antibodies against it in the umbilical cord blood, breast milk, placentas and vaginas of some pregnant infected women, another suggestion that the virus can be passed to fetuses and newborns, according to results of a small study released Thursday.

Just two of the infants in the sample examined by Italian researchers tested positive for the virus, and both quickly recovered. In one case, a baby tested negative two days later, an indication that the child was already producing antibodies against the virus in the womb, said Claudio Fenizia, an assistant professor of immunology at the University of Milan, who led the study.

In an interview, Fenizia said the review of 31 pregnant women is preliminary and was plagued by factors that make it too early to draw conclusions for use in the care of pregnant women infected by the virus. But, he said, “our study should be considered a ringing bell to raise awareness that [transmission] is possible.” He urged further research in the area, which is underway in some places.

The full study is not yet available. An abstract with results was released Thursday ahead of a one-day worldwide conference on covid-19 scheduled for Friday. Previous reports on a small number of infected women in China reached similar conclusions.

Diana W. Bianchi, director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, said she found the results inconclusive. It’s difficult to tell, even in cases in which a newborn tests positive, whether the child was contaminated by bodily fluids from an infected mother during vaginal delivery or Caesarean section, she said.

A May study by Northwestern University researchers that showed damage to the blood vessels in 16 placentas is more troubling, she added. The study found insufficient blood flow from mother to fetus and blood clots in vessels of the placenta.

Bianchi’s institute, part of the National Institutes of Health, is funding a review of the records of births this year to help determine the virus’s impact on pregnant women and newborns. Records from March to December 2020 will be compared with records from the same period of 2019 to see whether the virus caused consistent medical problems in pregnant women, she said.

Fenizia’s group looked at 31 women with the coronavirus in three Milan-area hospitals in March and April. All were late in their pregnancies, leaving open the question of the virus’s impact on the early stages of gestation.

The virus itself was found in one woman’s vagina, one woman’s placenta, one woman’s umbilical cord blood and one woman’s breast milk, the results show. Nine had antibodies in umbilical cord blood and one showed them in breast milk.

Fenizia said the results suggest it may be important as the pandemic continues to monitor pregnant mothers and newborns for signs of inflammation, especially following the discovery of an alarming inflammatory syndrome linked to covid-19 that has affected hundreds of children in the United States.

At the moment, he said, there are no proven interventions for pregnant women infected by the coronavirus. Fenizia said prevention is the best approach.

In its guidance for pregnant women, the Centers for Disease Control and Prevention notes that pregnant women “might be at increased risk for severe illness” from covid-19.