Over 500 hospitals have closed their labor and delivery departments since 2010, according to a large new study, leaving most rural hospitals and more than a third of urban hospitals without obstetric care.

Those closures, the study found, were slightly offset by the opening of new units in about 130 hospitals. Even so, the share of hospitals without maternity wards increased every year, according to the study, published on Wednesday in JAMA, a prominent medical journal. Maternal deaths remained persistently high over that period, spiking during the pandemic.

Because its data runs only through 2022, the study does not account for the additional challenges that hospitals have faced since the Supreme Court case that overturned Roe v. Wade that year and led many states to restrict abortion. States with abortion bans have experienced a sharp decline in their obstetrician work force.

“We’re more than a decade into a severe maternal mortality crisis in the United States, and access to hospital-based maternity care has continued to decline over that entire time period,” said Katy Kozhimannil, the study’s lead author and a professor of health policy at the University of Minnesota.

Other research from Dr. Kozhimannil and her colleagues has found that the closures of rural maternity wards can lead to an increase in births in emergency rooms or outside of hospitals.