London (CNN)More than half of pregnant women admitted to UK hospitals with Covid-19 were from black or other ethnic minority groups, according to a national study published Monday in the BMJ medical journal.
Researchers led by the University of Oxford’s Nuffield Department of Population Health warned that although transmission of the virus to infants was uncommon and most women had “good outcomes,” the high proportion of infected women from black or minority backgrounds “needs urgent investigation and explanation.”
A separate government review by Public Health England found last week that members from the UK’s ethnic minority communities are up to 50% more likely to die with coronavirus than their white British peers.
The latest study is based on data from the UK’s Obstetric Surveillance System, a national system established to study a range of rare disorders of pregnancy.
The researchers said that of 427 pregnant women admitted to hospital with Covid-19 between March 1 and April 14, more than half were from minority groups, including 25% who were Asian and 22% who were black.
Most of the women were in their late second or third trimester, 70% were overweight or obese, 40% were aged 35 or over, and a third had pre-existing conditions, the researchers said.
The study noted that while published evidence on the rate, transmission and effect of coronavirus infection in pregnancy is limited, some evidence had suggested that pregnant women and their babies are at greater risk of severe illness and death.
However, an April study published in the American Journal of Obstetrics & Gynecolocy found that the majority of pregnant women who are diagnosed with coronavirus don’t experience more severe illness than the general population.
Twelve babies born to mothers in the study tested positive for coronavirus, six of them within the first 12 hours of their lives.
UK Health Secretary Matt Hancock has warned that being black or from a ethnic minority background was a “major” Covid-19 risk factor.
In an address to parliament last week, Hancock said there was “much more work to do to understand the key drivers of these disparities, the relationships between the different risk factors and what we can do to close the gap.”
Public Health England’s analysis found that the link between ethnicity and health was “complex and likely to be the result of a combination of factors.”
“Firstly, people of BAME [black and minority ethnic] communities are likely to be at increased risk of acquiring the infection,” the government review said, noting that minorities are more likely to live in urban areas, in overcrowded households, in deprived areas, and have jobs that expose them to higher risk.
“People of BAME groups are also more likely than people of white British ethnicity to be born abroad, which means they may face additional barriers in accessing services that are created by, for example, cultural and language differences,” it added.
The groups are “also likely to be at increased risk of poorer outcomes once they acquire the infection,” the agency’s report found.
UN High Commissioner for Human Rights Michelle Bachelet also warned that Covid-19 had exposed inequalities within society and was having a disproportionate impact on racial and ethnic minorities, including people of African descent.
CNN’s Zamira Rahim contributed to this report.