She is arguably one of the best tennis players of all time. She is widely popular, even among non-sports fans and is married to the multi-millionaire co-founder of Reddit. Yet, after the birth of her first child, Serena Williams tells Vogue she had to convince health care professionals to take her seriously when she noticed signs of a pulmonary embolism.

As recounted in Vogue:

“The nurse thought her pain medicine might be making her confused. But Serena insisted, and soon enough a doctor was performing an ultrasound of her legs. ‘I was like, a Doppler? I told you, I need a CT scan and a heparin drip,’ she remembers telling the team. The ultrasound revealed nothing, so they sent her for the CT, and sure enough, several small blood clots had settled in her lungs. Minutes later she was on the drip. ‘I was like, listen to Dr. Williams!’”

That this could happen to Williams paints a bleak picture of maternity care in the United States, where more women die of pregnancy-related complications than in any other developed country. The statistics are even worse for black women, who die at three to four times the rate of white women from childbirth, according to the most recent statistics from the Centers for Disease Control and Prevention.

What’s even more heartbreaking is that two leading causes of maternal death—preeclampsia and hemorrhage—are preventable. So what is going on?

The challenge facing African-American mothers is a complex one, with a deadly interplay of genetic and sociocultural factors at work. Black women are more susceptible to chronic illnesses such as anemia, obesity, hypertension and diabetes, which can complicate an otherwise normal pregnancy.

For the estimated 45% of women experiencing an unplanned pregnancy, there is often a delay in managing pre-existing conditions such as these—and that’s if they have access to prenatal care at all, given that black women are less likely to be insured than white women.

Once African-American women make it into care facilities, their concerns are often dismissed by professionals, just as Williams experienced.

“We know there are instances where [African-American mothers] are not given the proper level of attention and care because of assumptions that doctors and hospitals are making about them,” Shawn Theirry, a Texas House of Representatives member who recently introduced legislation that would investigate this discrepancy, tells the Los Angeles Times.

When a “violent reaction” to an epidural threatened her own life during childbirth, Thierry says it was only because of her “excellent insurance” that she got the care she needed.

But, for many more, that is not the case—as a recent investigation from ProPublica and NPR reveals. As the report recounts:

“In the more than 200 stories of African-American mothers that ProPublica and NPR have collected over the past year, the feeling of being devalued and disrespected by medical providers was a constant theme. The young Florida mother-to-be whose breathing problems were blamed on obesity when in fact her lungs were filling with fluid and her heart was failing. The Arizona mother whose anesthesiologist assumed she smoked marijuana because of the way she did her hair. The Chicago-area businesswoman with a high-risk pregnancy who was so upset at her doctor’s attitude that she changed OB-GYNs in her seventh month, only to suffer a fatal postpartum stroke.”

Another threat of implicit bias is that physicians often fail to appreciate the complexities within the label of “black” that is assigned to persons of color—which can blind them to diagnoses they don’t believe are common for black people.

That was the case for Shalon Irving, a lieutenant commander of the US Public Health Corps and an epidemiologist at the CDC, who died three weeks after her daughter’s birth from a blood clot disorder most common among those of European descent.

As a dark-skinned woman, she had never been tested for the illness—even though multiple members of her family had died from symptoms that clearly implicated it. The illness, apparently, didn’t know that they were black. Nor did it realize that Irving was educated, middle class and insured.

There’s a final major factor at play here, and it’s the United States’ attitude towards pregnancy itself.

This country often focuses on fetal and infant care to the detriment of the mother. Pregnancy is treated as pathology, with C-sections, epidurals, inductions and other interventions at an all-time high.

Compare that to the United Kingdom, where every maternal death is painstakingly evaluated to hold caretakers culpable and promote the sharing of data that could prevent future tragedies. In the United States, this maternal mortality review process is left to the discretion of states—of which 24 have procedures in place, according to a 2017 report in the journal Obstetrics & Gynecology.

Without these processes, there is no way to learn from mistakes. And the price we pay for that is women’s lives.

More must be done by our government and caregivers to empower the medical community to listen and look carefully at its patients as people—not statistics, presumptions or stereotypes.

Williams helped drive that conversation when she was so open about her experience, which has already led to an outpouring from women with similar stories. In a Facebook post this week, Williams said she is humbled, grateful and optimistic because of these responses.

“I want to thank all of you who have opened up through online comments and other platforms to tell your story,” she says. “I encourage you to continue to tell those stories. This helps. We can help others. Our voices are our power.”