Medical professionals have spotted a number of instances of newborn babies having contracted the Covid-19 - with one such case noted by researchers in China back in February.
However doctors at the Antoine Beclere hospital in Paris were able to confirm a child was a carrier of the virus just one hour after its birth - and believe the infection may have passed through the placenta in utero.
Outlining their case study in journal Nature Communications, researchers said a pregnant 23-year-old was admitted to hospital in March with a fever and severe cough.
After testing positive for Covid-19, her baby was born three days later by caesarean. Tests one hour after birth, then again three and 18 days later, all showed positive results for the presence of the virus.
Additional tests of fluid taken from the newborn’s lungs - as well as blood samples - also showed signs of the virus.
And researchers found the baby had presented with some of the neurological symptoms associated with the virus that have been seen in adults - with neuroimaging analyses indicating white matter injury, which can be caused by vascular inflammation the Sars-CoV-2 infection causes.
However while questions have remained over how the virus could spread in utero - between an environmental or cervical route, or through the placenta - scientists believe they may have narrowed in on the source.
Along with his colleagues, Daniele De Luca, medical director of paediatrics and neonatal critical care at the Antoine Beclere, measured higher viral loads in the placenta than in the amniotic fluid and maternal blood - suggesting Sars-CoV-2 might actively replicate in the cells inside the placenta.
However researchers say that further studies will be needed to confirm these results.
Writing in Nature Communications, they said: "We report a proven case of transplacental transmission of Sars-CoV-2 from a pregnant woman affected by Covid-19 during late pregnancy to her offspring.
"Other cases of potential perinatal transmission have recently been described, but presented several unaddressed issues."
Both mother and child have recovered from their infections, and were later discharged from hospital.
The researchers added: "In conclusion, we have demonstrated that the transplacental transmission of Sars-CoV-2 infection is possible during the last weeks of pregnancy.
"Transplacental transmission may cause placental inflammation and neonatal viremia.
"Neurological symptoms due to cerebral vasculitis may also be associated."
Additionakl reporting by PA