Statistics show that the United States posts the worst maternal mortality rate in the developed world. What’s more, according to the Centers for Disease Control and Prevention (CDC), Black mothers are three to four times more likely to die following childbirth than their white counterparts, reports NPR.

In a series titled “Lost Mothers: Maternal Mortality in the U.S.,” NPR and ProPublica explored the factors responsible for the high maternal mortality rate in the United States. (Maternal mortality refers to death during the maternal period, which the CDC defines as the time between the start of a pregnancy to a year after delivery or termination.) During the investigation, reporters from the two agencies learned that the dying of African-American mothers was the main reason for the overall uptick in the maternal mortality rate in the United States when compared with other affluent countries.

Interestingly, the inquiry showed that even Black women who are relatively well off are at a higher risk of death from pregnancy or childbirth compared with white women. (A 2016 study found that Back college-educated women who gave birth in local hospitals were more likely to suffer severe complications from childbearing than white women who didn’t complete high school.)

Researchers suggest that racism is partly to blame for these large disparities. One factor is that the hospitals where Black mothers give birth are often products of historical segregation that provide low-quality care and have significantly higher rates of life-threatening complications.

In a survey conducted earlier this year by NPR in conjunction with the Robert Wood Johnson Foundation and the Harvard T.H. Chan School of Public Health, 33 percent of Black women reported feeling discriminated against by their doctors because of their race. Additionally, 21 percent of African-American mothers-to-be avoided physicians altogether because they feared racial discrimination. Many expectant and new Black mothers also felt that their providers didn’t take their pain seriously. (Numerous studies have shown that doctors frequently undertreat pain among their Black patients.)

But the discrimination Black women face in other areas of their lives may register the biggest effect on poor maternal outcomes by causing chronic stress, which ultimately can negatively affect pregnancy and childbirth.

Experts believe that discussions should focus on postpartum care because more than half of maternal deaths occur after childbirth. For Black mothers, sporadic postpartum care is key as these women are more likely to suffer from hypertensive disorders and peripartum cardiomyopathy (pregnancy-induced heart failure), among other problems.

Click here to learn how minorities are more likely to receive low-value health services.