Doctors in the central Chinese city of Wuhan have found no evidence that mothers with COVID-19 can transmit the virus to their children during pregnancy. The results of their study were published Monday in the scientific journal Frontiers in Pediatrics.

While the novel coronavirus that causes COVID-19 has mostly spared young children, whether infected mothers can pass the virus to their babies during pregnancy has remained unclear. Experts raised concerns over “possible vertical transmission from mother to infant” after a case in Wuhan of an infected woman’s infant testing positive for the virus 30 hours after birth.

To investigate the issue further, doctors at Wuhan Children’s Hospital and Wuhan Union Hospital studied four pregnant women with COVID-19. All were diagnosed during their final trimester of pregnancy, and each gave birth to a full-term baby.

All of the newborns were isolated from their mothers immediately after birth and fed with formula. Doctors ran nucleic acid tests for three of the babies, while the fourth baby’s guardians refused the test.

The three tests were negative for the coronavirus, and none of the babies, including the untested one, exhibited typical symptoms of COVID-19 such as fever or cough — though one experienced some difficulty breathing after birth. That baby had tested negative, and a chest radiograph showed different features from COVID-19. He was diagnosed with transient tachypnea of the newborn — a temporary and not-uncommon condition potentially caused by the delayed clearing of fetal lung fluid. The infant had recovered by day four.

The results of Monday’s study are consistent with retrospective reports from two research teams published in the journals Translational Pediatrics on Feb. 10 and The Lancet on Feb. 12. Each team studied nine mothers and their newborns in Hubei province, where Wuhan is located, and found no evidence that the virus could cross the placenta and infect babies during pregnancy.

The Lancet study also tested infected mothers’ amniotic fluid, umbilical cord blood, and breast milk, in addition to administering nucleic acid tests for the newborns, all of which came back negative. The most recent study did not conduct this full spectrum of tests.

The authors of Monday’s study acknowledged that nucleic acid tests are not always reliable in diagnosing COVID-19. Current data suggests that the test is accurate in 70% of cases, the team said in their paper. “Therefore, the reliability of diagnostic test should be further evaluated especially for children,” they wrote.

“So far, the literature does not suggest a role for mother-to-newborn transmission during pregnancy or delivery,” Megan Freeman, a pediatric infectious disease doctor at the University of Pittsburgh’s School of Medicine, told Sixth Tone. “Some newborns have acquired COVID-19 after being born... but that is most likely through respiratory droplets or close contact with infected family members.”

Experts say that because there are so few cases of infants born to mothers with COVID-19, it’s hard to draw definitive conclusions for now. “This is not a situation where we can design an experiment and control sample size,” Freeman said. “We must learn from the instances that exist as best we can.”

The placenta can keep many viruses, including HIV, from contacting the unborn baby, but it’s not an ironclad system: Some pathogens such as the rubella virus can pass through and infect the fetus.

“There is still much to learn about what allows some pathogens in and keeps other pathogens out,” Freeman said.

Editor: David Paulk.

(Header image: E+/VCG)