Chinese scientists report that it is possible – though rare – for pregnant women infected with COVID-19 to transmit the illness to their newborn in what is the largest case-series of infected mothers to date. Though less than one-in-ten infants were found to be infected, the findings present an important opportunity to study the potential implications of mother-to-newborn transmission.

It comes after a newborn baby in London became one of the youngest cases in the world to test positive for SARS-CoV-2, the virus responsible for COVID-19. Prior to that, a baby in China tested positive at just 30 hours old.

Researchers followed 33 pregnant women infected with COVID-19 at Wuhan Children’s Hospital in Wuhan, China, where the pandemic is believed to have originated. In the very small sample size, three male babies delivered by cesarean tested positive for the infection within two days of being born. One baby was prematurely delivered at 31 weeks due to fetal distress that required resuscitation.

The two babies born at-term were treated in neonatal intensive care units for lethargy and fever. Chest radiographs showed evidence of pneumonia, but by day six both were cleared of the virus and tested negative. The baby born prematurely suffered the most severe illness and was treated in intensive care for sepsis, neonatal respiratory distress syndrome, and pneumonia confirmed by chest radiographs. Test results indicated that the virus had cleared on the seventh day following ventilation, antibiotics, and caffeine treatment. Symptoms were shown to resolve within two weeks.  

All babies survived.

"Because strict infection control and prevention procedures were implemented during the delivery, it is likely that the sources of SARS-CoV-2 in the neonates' upper respiratory tracts or anuses were maternal in origin,” write the study authors in JAMA Pediatrics.

Some experts disagree, arguing it is more likely that the babies became infected after birth.

“There is still no conclusive evidence that COVID-19 is contracted in the womb and it is more likely that the infants were exposed during or immediately after delivery,” said Dr Elizabeth Whittaker, a consultant in Pediatric Infectious Diseases at St Mary’s Hospital Paddington and member of the RCPCH COVID-19 Expert Advisory Group, in a statement. Whittaker was not involved in the study.

Because the babies were first shown positive at two days, Paul Hunter, a professor in Medicine at the University of East Anglia (UEA) who was not involved in the study, suspects that the babies were “infected after being brought into the world rather than in the womb.” Additionally, two previous studies have demonstrated no clinical findings that newborns born to affected mothers can also become infected.

A small case study previously determined that infected mothers cannot transmit COVID-19 to newborns, though the findings suggest that “vertical transmission” from mother to child could occur across the placenta or during the process of childbirth. The researchers add that their findings present an important opportunity for future research, and highlights the need to screen pregnant women and monitor their babies

"Therefore, it is crucial to screen pregnant women and implement strict infection control measures, quarantine of infected mothers, and close monitoring" of newborns,” the team concluded.

The Centers for Disease Control and Prevention notes that COVID-19 is a new disease and experts are still learning about how it spreads. It is unknown whether pregnant women have a greater chance of getting sick, if an infection can be passed to the fetus, or whether maternal illness will cause problems or adversely affect the health of the baby after birth. The best way pregnant women can protect themselves is by practicing social distancing and healthy hygiene habits.