The United States was already struggling with one of the worst maternal mortality rates of any industrialized nation when the onset of the COVID-19 pandemic saw them rise even higher—particularly during the pandemic’s second year—exacerbating racial and ethnic disparities, new University of Maryland research has found.

The study, published yesterday in Obstetrics & Gynecology, found pregnancy-related deaths climbed to 45.5 per 100,000 live births in 2021, up from rates of 36.7 in 2020 and 29 pre-pandemic. The deaths include people who died while pregnant or within one year of the end of their pregnancy due to a condition related to or aggravated by the pregnancy.

Marie Thoma, lead author and an associate professor in the School of Public Health’s Department of Family Science, said that while researchers could not isolate the role COVID-19 played, the increase was consistent with the rising rates of the virus associated with death among women of reproductive age.

Thoma’s publication with Eugene Declercq, professor of community health sciences at Boston University’s School of Public Health, coincided with the release yesterday of a National Center for Health Statistics report that found a 38% spike in maternal deaths during pregnancy and in the first six weeks following the end of pregnancy in 2021, compared to 2020.

Pregnant and recently pregnant people are a particularly vulnerable population, as they are already at increased risk of severe illness with COVID-19.

“Our previous research examined the increases in maternal death in 2020, after the pandemic started, so I was hopeful we would see a decline because of vaccinations and other factors in 2021,” Thoma said. “But it’s not what we saw. Instead, we saw more pregnant and recently pregnant people dying and the emergence of the more transmissible, aggressive Delta variant.”

According to the CDC, only 31% of pregnant people were fully vaccinated before or during their pregnancy as of September 2021.

All races and ethnicities experienced an increase in pregnancy-related deaths in 2021, with the rate reaching as high as 56.9 per 100,000 births from July to September (when the Delta variant peaked). Pregnancy-related death rates rose more for Hispanic and Black people than White and Asian people, but American Indian/Alaska Native people were hardest hit, experiencing 160.8 deaths per 100,000 births—more than double their pre-pandemic rate. The American Indian/Alaska Native population also experienced high rates of COVID-19 mortality in 2021.