The number of people dying in the U.S. from pregnancy-related causes has more than doubled in the last 20 years, according to a new study, published in JAMA, the Journal of the American Medical Association.

And while the study found mortality rates remain "unacceptably high among all racial and ethnic groups across the U.S.," the worst outcomes were among Black women, Native American and Alaska Native people.

The study looks at state-by-state data from 2009 to 2019. Co-author Dr. Allison Bryant, an obstetrician and senior medical director for health equity at Mass General Brigham in Boston, says maternal death rates in the U.S. just keep getting worse.

"And that is exacerbated in populations that have been historically underserved or for whom structural racism affects them greatly," she says.

Maternal death rates have consistently been the highest among Black women, and those high rates more than doubled over the last twenty years. For Native American and Alaska Native people, the rates have tripled.

Dr. Gregory Roth, at the University of Washington, also co-authored the paper. He says efforts to stop pregnancy deaths have not only stalled in areas like the South, where the rates have typically been high. "We're showing that they are worsening in places that are thought of as having better health," he says.

Places like New York and New Jersey saw an increase in deaths among Black and Latina mothers. Wyoming and Montana saw more Asian mothers die. And while maternal mortality is lower for white women, it is also increasing in some parts of the country.

"We see that for white women, maternal mortality is also increasing throughout the South, in parts of New England and throughout parts of the Midwest and Northern Mountain States," he says.

The steady increase in maternal mortality in the U.S. is in contrast to other high-income countries which have seen their much lower rates decline even further.

"There's this crystal clear graph that's been out there that's very striking," Bryant says. With countries like the Netherlands, Austria and Japan with a clear decrease. "And then there is the U.S. that is far above all of them and going in the opposite direction," she says.

These other wealthy countries, with lower death rates for new mothers, approach the problem differently, says Dr. Elizabeth Cherot, chief medical and health officer at the maternal health nonprofit March of Dimes. "They wrap services around new mothers. They give them [support for] everything from mental health, cardiovascular, diabetic, pelvic health. These things are just considered standard," but are not universally offered to individuals postpartum in the U.S.

Most maternal deaths are deemed preventable by state review committees. Dr. Catherine Spong, at the University of Texas Southwestern Medical Center, says pregnancy-related deaths can be caused by different things. The biggest risk factors are conditions like cardiovascular disease, severe pre-eclampsia, maternal cardiac disease and hemorrhage, she says.

Continuing heart problems and mental health conditions can also contribute to the death of a new mother.

The researchers say doctors would have a better chance of dealing with these health conditions, if more women had access to healthcare after their babies were born.

About half the births in the U.S. are paid for by Medicaid and "the majority of the deaths are in the immediate postpartum period," Roth says. "If you don't have easy access to health care in this period, you're at very high risk."

For those who get their healthcare through Medicaid, medical coverage lasts at least two months after the birth of a child. Since 2021, states have had the option to extend that coverage for a year. So far, 35 states and Washington D.C. have done so.