For the first time, the United States has standardized maternal mortality data from all 50 states — a first step toward identifying ways to reduce pregnancy-related deaths across the country, experts say.

The data, released Thursday by the National Center for Health Statistics, show that the national maternal mortality rate — deaths caused or aggravated by pregnancy — was an estimated 17.4 maternal deaths per 100,000 live births in 2018, when 658 women died.

The new statistics are similar to figures from the Centers for Disease Control and Prevention, the umbrella agency for the National Center for Health Statistics. The CDC has found that about 700 women die from complications related to pregnancy or childbirth every year, putting the U.S. in last place among all developed nations in terms of maternal mortality.

What differentiates the new data is the degree of certainty with which researchers believe it to be accurate: In 2003, the National Center for Health Statistics recommended that all states add a standardized checkbox for maternal deaths after researchers noticed that many of them were not being coded properly, resulting in some being underreported and others being overreported.

"It made it impossible to make any sense of trend at the national level," said Bob Anderson, chief of the mortality statistics branch at the National Center for Health Statistics.

It is a critical statistic to get right, Anderson added.

"Maternal mortality is an important indicator of the health of a nation," he said. "These are deaths that are almost entirely preventable, and these are deaths that are occurring at a time that is supposed to be about birth, not death, so it's particularly poignant when a mother dies in childbirth."

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Because of constraints in funding and the limits of technology and state laws, it wasn't until 2017 that all states had added the standardized maternal mortality checkbox to their vital registration systems. (California is the last state to do so; it implemented a different checkbox that was usable for the purposes of the National Center for Health Statistics report, Anderson said, but it will switch to the standardized checkbox later this year.)

Using the new coding method, researchers found that of the 658 women who died of maternal causes in 2018, black women fared the worst, dying 2½ times more often than white women (37.1 vs 14.7 deaths per 100,000 live births), while Hispanic women had the lowest rate of maternal mortality, 11.8 deaths per 100,000 live births.

Black women have historically had the highest maternal mortality rates. Researchers do not have a clear explanation, but they suspect a combination of institutional racism in society and the health care system, as well as black women's increased susceptibility to certain health conditions, such as obesity and hypertension. Black women are also less likely to have access to quality prenatal care.

Figures from the CDC's Pregnancy Mortality Surveillance System indicate that from 2007 to 2016, black mothers died at a rate of 3.2 times that of white mothers; in that dataset, Hispanic mothers also had the lowest rate, at 11.5 pregnancy-related deaths per 100,000 live births, slightly less than white women's rate of 12.7 pregnancy-related deaths per 100,000 live births.

The two datasets use slightly different methodologies: The CDC's Pregnancy Mortality Surveillance System defines a pregnancy-related death as happening within a year of pregnancy, while the National Center for Health Statistics uses the World Health Organization's definition of 42 days within pregnancy.

While the National Center for Health Statistics' data are the most recent, Anderson cautioned that they are only a first look at 2018 maternal deaths and cannot be guaranteed to be 100 percent reliable, even with the changes. He said the Pregnancy Mortality Surveillance System is expected to dive into the data more deeply in the future.

Regardless, he said, the new information solidifies what women's health advocates have already zeroed in on as a crisis: the high rate at which black mothers are dying during or after childbirth.

“I don’t think it’s as important to focus on the exact numbers. What’s important is that black women have a much higher maternal mortality rate than white women.”

"That's really the takeaway," Anderson said. "I don't think it's as important to focus on the exact numbers. What's important is that black women have a much higher maternal mortality rate than white women."

The report did not break down deaths by other races.

Nonetheless, advocates hailed the new data as an important step.

"We have to understand the problem in order to solve it," said Monifa Bandele, senior vice president of MomsRising, a nonprofit organization that advocates for the rights of mothers and other women. "And we never had consistent data, so there was really no way to quantify what was happening. But what we did know from the data that we were getting was that there is a crisis."

“We have to understand the problem in order to solve it.”

She and others said they hoped more precise data could lead to new policies that would reduce preventable deaths and eliminate the racial disparity in maternal mortality.

"Data from the NCHS reflects the scale of the public health challenge we face," Dr. Maureen Phipps, chief executive of the American College of Obstetricians and Gynecologists, the nation's leading group of women's health care physicians, said in a statement. "Access to reliable, consistent data year after year is critical to establishing benchmarks, setting goals, and measuring progress towards improving outcomes."