The study looked at 427 pregnant women admitted to 194 hospitals across the UK between 1 March and 14 April 2020 with confirmed COVID-19. It found found that 4.9 pregnant women per 1,000 were admitted and around one in 10 of these received intensive care. This suggested 'that pregnant woman are at no greater risk of severe illness than the non-pregnant population,' the researchers said.
However, the researchers found that the majority of pregnant women who did require hospitalisation for COVID-19 were in their third trimester, which they said emphasised the importance of social distancing in this group.
The findings also showed that pregnant women from black, Asian and minority ethnic (BAME) backgrounds were more likely to be admitted to hospital for COVID-19. Older pregnant women, those who were overweight and obese and those who had a pre-existing medical problem, were also more likely to be admitted to hospital.
BAME women at increased risk
The researchers said that these patterns were 'similar to those in the general population hospitalised with Sars-CoV-2'. However, they added that the results relating to BAME women were concerning and required 'urgent investigation and explanation'.
'Our sensitivity analysis suggests that this cannot simply be explained by higher incidence in the main metropolitan areas with higher proportions of women from ethnic minority groups, as evidence of effect persisted when women from London, the West Midlands and the North West were excluded,' the study said. 'The effect also persisted despite adjustment for age, BMI and co-morbidities.'
Public Health England is set to report at the end of May on how ethnicity, gender and obesity affect COVID-19 risk, after the government accepted the need for an investigation into disproportionate deaths among people who are BAME. Research published last week found that the risk of death from COVID-19 is two to three times higher for people from BAME groups compared with the general population.
Impact on infants
One in five babies born to the mothers in the study were born premature and admitted to a neonatal unit. One in twenty babies born had a positive test for COVID-19, but only half of these babies had positive test immediately after birth.
The researchers highlighted that they did not have full pregnancy outcomes for all of the women who were admitted and later discharged when well, but they said outcomes 'for infants are largely reassuring when considering potential impacts of SARS-CoV-2 infection acquired before or during birth'.
'The small number of early PCR positive infants of mothers with infection did not have evidence of severe illness,' the study said.
'Nevertheless, 2% of infants did have evidence of viral RNA on a sample taken within 12 hours of birth, which suggests that vertical transmission may be occurring. We have no evidence as to whether IgM was raised in these infants and therefore whether infection was acquired before or during birth, but three infants tested positive following pre-labour caesarean section.'
They said the findings emphasised the importance of infection control measures around the time of birth.
The study was conducted by the University of Oxford in collaboration with the Royal College of Obstetricians and Gynaecologists, the Universities of Leeds and Birmingham, Kings and Imperial Colleges London.