Of all 211 maternal deaths in Colorado between 2004 and 2012, 30 percent were attributed to self-harm. That included suicides and drug overdoses -- most often in the year after a woman gave birth.
Self-harm was the most common cause of maternal deaths -- ahead of car accidents, medical conditions and homicide, the researchers said.
It's not clear whether self-harm deaths are becoming more common, said lead researcher Dr. Torri Metz, a maternal-fetal medicine specialist at Denver Health Medical Center.
Nor is it known whether other U.S. states are showing the same pattern, she said.
But the results underscore the importance of screening pregnant women for depression, according to Metz.
Guidelines from the American College of Obstetricians and Gynecologists (ACOG) say that all women should be screened at least once for "perinatal" depression -- symptoms that occur during pregnancy or in the first year after a woman gives birth.
But it's not clear how often that actually happens in the real world, Metz said.