Medicine continues to advance on many fronts, yet basic health care fails hundreds of women a year who die during or after pregnancy, especially women of color. Black mothers die at a rate that's 3.3 times greater than whites, and Native American or Alaskan Native women die at a rate 2.5 times greater than whites, according to a report out this week from the Centers for Disease Control and Prevention.

Yet, the report concluded, roughly 3 in 5 pregnancy-related deaths are preventable. The racial disparity in maternal death rates is a dramatic argument for prevention efforts that address diverse populations, says Dr. Wanda Barfield, director of the Division of Reproductive Health and assistant surgeon general in the U.S. Public Health Service.

About 700 women died each year from complications of pregnancy in the U.S. between 2011 and 2015, either while pregnant or up to a year after delivery.

The CDC's principal deputy director, Dr. Anne Schuchat, notes that every death reflects a web of lost opportunities including lack of access to health care, missed or delayed diagnoses, and failures by doctors or nurses to recognize warning signs.

"Big-picture, system-related changes are needed," Schuchat said in a press briefing. She noted the process won't be easy and could require remaking systems that have been in place for years.

The CDC says health care providers need to help patients better manage chronic conditions that could be exacerbated by pregnancy. More than a third of pregnancy-related deaths were due to cardiovascular conditions, according to the CDC report.

Women who died during childbirth itself typically suffered severe bleeding or what's called an amniotic fluid embolism, where amniotic fluid leaks into the mother's bloodstream.

During the week after delivering their babies, women who died experienced severe bleeding, extremely high blood pressure or infection.

And during the year after having their baby, women died from complications of hypertension, stroke or a weakening of the heart muscle, called cardiomyopathy.

Pregnant and postpartum women need to understand warning signs so they can identify problems early on and seek timely treatment, the CDC report warns. For hospitals and health systems, the CDC says medical responses to emergencies should be standardized so providers are crystal clear about how to proceed with treatment.

When addressing racial disparities, it's important to note the difference in underlying chronic disease risk, Barfield says. Cardiovascular disease is more common among black women and can occur at earlier ages than in white women, she says. It may be that cardiovascular symptoms are never identified in these women or that they simply cannot overcome social factors such as a lack of transportation to access health care, she says.

In addition, Barfield says that some inequities can be explained by variation in hospital quality. "This can mean that effective interventions may not be occurring for black women," she says, or that the timing of the intervention may not be appropriate.

"Minority women are delivering in different and lower-quality hospitals than white women," she says, adding that this could clearly affect outcomes.

Barfield suggests doctors and other health care workers "cross communicate" and discuss potential weaknesses in the system to shore up better prenatal and postnatal care for minorities. "There's a perception among many black women that the care they receive during and after pregnancy is different than it is for their white counterparts," she says.

There is "an implicit racial bias in health care," Barfield says, and black women often feel they are not being heard when they raise concerns about a particular aspect of their care.

Today it's becoming more clear that disparities have more to do with racism than race, says Neel Shah, an OB-GYN and a professor at Harvard Medical School.

For a long time there was "this baked-in assumption" that there was something different genetically among black women leading to their higher rates of maternal mortality, he says. But "genetically we are all the same," he says, and the evidence is strong that it is the chronic effect of the stress of racism, or "weathering" as some researchers describe it, that takes its toll on pregnancy, childbirth and care for a newborn after birth.

And this stress can take place in medical settings as well, where unconscious bias can affect quality of care, according to NPR's 2017 investigative report. NPR and ProPublica collected 200 stories from African American mothers and found that unconscious bias in health care was a "constant theme."

What's more, racial disparities and the increased risk for black women are not ameliorated by social status, income or education, says Shah.

The story of tennis star Serena Williams is an example of that. In the days after giving birth to her daughter, Williams developed a life-threatening pulmonary embolism, or blood clots in the lung, as she told Vogue last year.

There is some progress being made in addressing maternal mortality, says the CDC's Schuchat. Many states and local communities nationwide have already implemented changes that could "serve as a model for the nation" to make a difference in pregnancy-related death. So far, 13 states have taken the lead, and Schuchat hopes to expand these programs to other states.

And there is growing awareness of the issue in the private sector and among physicians. Shah co-founded , a coalition of more than 20 organizations dedicated to increasing public and private investment in the well-being of mothers. The organization has a march planned in Washington, D.C., on May 11.

The American College of Obstetricians and Gynecologists recently published Practice Bulletin, Pregnancy and Heart Disease, which offers guidance to doctors about screening, diagnosis and management of heart disease for women during pregnancy and the postpartum months.

Bringing down maternal mortality rates will require a concerted, communitywide effort, Schuchat notes.

"We have the means to identify problems and close gaps and prevent deaths," Schuchat said.

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