Doctors are studying the impact of COVID-19 on unborn babies in Singapore, where an infant delivered by an infected mother earlier this month had antibodies against the virus but did not carry the disease.

The ongoing study among the city-state’s public hospitals adds to international efforts to better understand whether the infection can be transferred during pregnancy, how babies develop antibodies in the womb and whether they offer an effective shield against the virus.

The National University Hospital, another hospital involved, said the study aims looks at the effects of COVID-19 on pregnant women, their fetus and outcomes after delivery.

The World Health Organization says while some pregnant women have an increased risk of developing severe COVID-19, it is not yet known whether an infected pregnant woman can pass the virus to her fetus or baby during pregnancy or delivery.

Doctors in China reported the detection and decline over time of COVID-19 antibodies in babies born to women with the coronavirus disease, according to an article published in October in the journal Emerging Infectious Diseases.

While there is evidence that transmission during pregnancy is rare, a small study in Italy suggested that it is possible, according to research published in the Nature journal in October.