Researchers confirm risk of COVID transmission from mother to unborn baby is very low

Research from UCL, UCLH and Great Ormond Street Hospital has confirmed that the risk of a mother passing on COVID to her unborn baby is very low.

The research, published in BJOG: An International Journal of Obstetrics & Gynaecology, should reassure women that if they have COVID—even if it is severe—it is unlikely their baby will be affected, and they should still give birth to a healthy baby.

First author, Dr. Charlotte Colley (UCL Institute for Women's Health and UCLH), said, "It was already thought that the risk of transmission was low, based on clinical observations made throughout the course of the pandemic.

"But through this research we were able to confirm these observations in a robust way, as we looked at a large number of women with varying severity of COVID symptoms, as well as looking at the effects of COVID infection that happened across all pregnancy trimesters."

In all, 244 women were involved in the research, which was led by Dr. Sara Hillman (UCL Institute for Women's Health and UCLH Consultant in Maternal and Fetal Medicine). Of these women, COVID infection was potentially passed through to the baby in just one case.

However, even in this one case reported, it is not clear when COVID was transmitted. The infection may have occurred at the time of delivery, because when the placenta was examined, it did not show any specific evidence of being affected by COVID (known as COVID placentitis), which would have been expected if infection had gone from mum via placenta to baby in the womb.

Furthermore, reassuringly, in the cases studied where COVID did seem to have affected the placenta and showed signs of placentitis (when analyzed by a specialist), the babies born to these women did not show any signs of COVID infection themselves after birth.

Dr. Hillman said, "The placenta is pretty protective against the baby getting COVID, thanks to the way it can acts as a barrier which prevents transmission from mum to baby in the womb."

While this study is reassuring and shows very low risk from maternal infection affecting the unborn baby, it is known that if women get COVID during their pregnancy then they themselves are often more unwell and can be at greater risk of severe outcomes such as having to go to the intensive care unit compared with women who are not pregnant.

This study gives pregnant women more reason to be vaccinated against COVID.