The placenta could mediate mother-to-baby COVID-19 transmission, according to new research.
A Swedish study reported on a pregnant woman who was hospitalised after suffering from sudden severe abdominal pain and who afterwards tested positive for COVID-19. Her fetus showed an abnormally low heart rate, which suggested that it was not getting enough oxygen. The baby was delivered by emergency caesarean section, and after two days tested positive for COVID-19. To investigate whether the baby had been infected when still in the womb, throat swabs from the mother and the newborn were analysed and compared.
'[Then] we analysed the virus strains in the baby, the mother and the placenta, and saw that they were almost identical. Since mother and child had not been cared for together for the first 48 hours, the similarity of the virus strains was another indication that the child was probably infected in the womb.' said Dr Anna Holmberg, specialist in infectious disease medicine and care hygiene at Skåne University Hospital, Malmo, Sweden.
Published in the British Journal of Obstetrics and Gynaecology, the study showed that mother-to-fetus COVID-19 transmission can occur through the placenta, resulting in placental inflammation and damage, and causing stress to the fetus. The placenta is a critical organ for the fetus' growth and wellbeing, as it provides oxygen and nutrients to the growing baby and removes waste products from its blood.
'We found that half the [placental] tissue was damaged.' Dr Mehreen Zaigham, first author of the study, told The Conversation. 'There was widespread inflammation, and we found coronavirus protein on both the mother's and foetus's side of the placenta. We also found coronavirus protein in all areas that were damaged by inflammation.' she added.
Previous research investigating coronavirus transmission through the placenta showed similar findings to the present study, reporting placental failure and baby's abnormal heart rate (see BioNews 1056). However, given the low incidence of mother-to-baby transmission in the womb, it seems to be a rare complication of COVID-19 during pregnancy. Scientists provide two explanations for this, one being the presence of the placental barrier – that protects the baby from most infections – and the second being the scarcity of the ACE2 receptor in the placenta, the key receptor needed for COVID-19 to enter the cells.
'Our findings suggest that perhaps we should rethink how we monitor pregnant women who have COVID, and they should be considered a more important risk group than we do today.' Dr Zaigham wrote in The Conversation.