Enlarge / A pregnant woman holds her belly on September 27, 2016. (credit: Getty | Matthew Horwood)

The number of people in the US dying of pregnancy-related causes more than doubled over two decades, with Black, Native American, and Alaska Native people facing the highest risks, according to a new study in JAMA.

The US has the highest rate of maternal deaths compared to other high-income countries, despite spending far more on health care—both on a per-person and share of gross domestic product basis. And, while US maternal deaths have long been high, they’ve only gotten higher while other high-income countries have seen declines.

Still, digging into US maternal mortality data to understand the trend is difficult. States define maternal deaths differently, some have been slow to add a standard pregnancy-related question on death certificates, and some delay the release of their data.