30 June 2023

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

It means pregnant women should feel reassured that if they have COVID – even if it is severe – it is unlikely their baby will be affected, and they should give birth to a healthy baby.

First author of the study Dr Charlotte Colley, Obstetrics and Gynaecology Speciality Registrar and Clinical Fellow/MSc student in Obstetric Ultrasound and Fetal Medicine at UCLH/UCL, 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 study, as we looked at a large number of women with varying levels of severity of COVID, as well as COVID cases in women across all pregnancy trimesters.”

244 women were involved in the research, which was led by UCLH Consultant in Maternal and Fetal Medicine Dr Sara Hillman, and published in the British Journal of Obstetrics and Gynaecology (BJOG).

Of these women, COVID infection was potentially passed through to the baby in just one case. The research team said the placenta acted as a barrier to transmission.

Even in the one potential case of transmission, it is not clear if COVID was indeed transmitted from mother to unborn baby. The infection in this case may have occurred at the time of delivery, because when the placenta was examined, it did not show any evidence of COVID.

Dr Hillman, who is also Professor at the Institute for Women’s Health at UCL, said: “We found that pregnancy is actually protective against the baby getting COVID, thanks to the way the placenta acts as a barrier which prevents transmission.”

While risk of transmission from mother to baby is very low, it is known that if pregnant women get COVID then they are often more unwell and can be at greater risk of outcomes such as having to go to the intensive care unit.

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

Read the paper in the BJOG: Routine placental histopathology findings from women testing positive for SARS-CoV-2 during pregnancy: Retrospective cohort comparative study

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