Scientists in China have said there is a chance Covid-19 may be passed from mother to baby during pregnancy, despite no direct evidence pointing to this method of transmission.

The babies born in Wuhan, China, were delivered by Caesarean section and experienced only mild symptoms that did not require intensive care treatment.

But authors concede there is no direct evidence of intrauterine vertical transmission, infections transmitted across the placenta, in the four cases.

Lead author Dr Zhi-Jiang Zhang, of Wuhan University, said: "Covid-19 is highly contagious and our study suggests that intrauterine transmission cannot be ruled out, but that the prognosis is good for both pregnant women and newborn babies."

Dr Zhang and his colleagues studied four newborns who were born between December 2019 and March 2020, three of whom were separated from their mothers at birth and were in isolation when symptoms occurred.

Two babies had fever, one had shortness of breath, one had cough while the fourth showed no symptoms.

Supportive treatment was provided for all four newborns.

Based on their findings, the researchers believe chances of infection through ways other than intrauterine transmission to be low, despite no traces of the virus being found in amniotic fluid or cord blood.

The team also said they could not rule out the possibility of the newborns being infected in hospital shortly after birth, although strict infection and prevention controls implemented during delivery make chances of hospital infection low.

The new research follows another study published last month in Jama Paediatrics, where scientists reporting on three newborns born at Wuhan Children's Hospital said they could not rule out intrauterine transmission of coronavirus.

Commenting on the findings, professor Tobias Welte, an infections expert from the European Respiratory Society and a coordinator for the national German Covid-19 task force who was not involved in the study, said: "It's important to protect pregnant women and newborn babies against infection.

"It's also important that any cases of Covid-19 in newborns are picked up, monitored and treated quickly and carefully.

"At this stage we still do not know whether there are any longer-term consequences of infection."