Can pregnant mom pass coronavirus to her unborn child? Early research says no.

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There are many unknowns about the new coronavirus, including whether pregnant women who catch the virus can pass it to their unborn child. Now, a preliminary study suggests the virus, known as 2019-nCoV, may not be transmitted during pregnancy.

However, the study was small and involved only pregnant women in the third trimester who gave birth via cesarean section (C-section). More studies are needed to confirm the findings and to see whether they apply to other groups of pregnant women, the authors said.

The study, published Wednesday (Feb. 12) in the journal The Lancet, follows the news of an infant in China who tested positive for 2019-nCoV within 36 hours of birth. But in that case, it wasn't clear whether transmission in the womb really happened, Zhang said. It may be that the infant caught the virus after birth from close contact, for instance, he said.

Some infections can pass from a mother to child during pregnancy, although exactly how this happens is often unclear. Pathogens may pass to the child through the placenta during pregnancy, or through contact with bodily fluids during delivery. For instance, if a pregnant woman has HIV, the newborn may become infected through blood that gets into the placenta during labor contractions, or through contact with blood during delivery, according to The American College of Obstetricians and Gynecologists. However, this mode of transmission is not very common among viruses, particularly respiratory viruses, according to The Guardian.

When the women gave birth via C-section, doctors collected samples of amniotic fluid, umbilical cord blood and breast milk, as well as samples from the newborn's throat. All of these samples were taken in the operating room at the time of birth so that they would best represent the conditions in the womb, the authors said

None of the women developed severe pneumonia as a result of their infection, and all of the newborns survived. What's more, none of the samples from the amniotic fluid, cord blood, breast milk or throat swabs tested positive for the virus.

"Findings from this small group of cases suggest that there is currently no evidence for intrauterine infection … in women who develop COVID-19 … in late pregnancy," the authors wrote.

Future studies "of pregnant women with COVID-19 infection, as well as neonates, will be necessary to ascertain the safety and health of mothers and babies" exposed to the new coronavirus, the authors concluded.

Originally published on Live Science.

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.