Rising maternal death rates in the U.S. may have been sharply overstated due to flawed record-keeping, according to new research that found mortality held steady and was in line with other developed nations over two decades.

Why it matters: Maternal health statistics have become a critical public health focus with millions of women living in areas with little to no access to maternity care and with more restricted access to abortion.

• But the study in the American Journal of Obstetrics & Gynecology concludes the 2003 inclusion of a checkbox on death certificates to show if a woman was pregnant at or close to the time of death has led to an increase in misclassified maternal deaths.

What they found: Researchers reviewed National Center for Health Statistics (NCHS) data from 1999 to 2021 and zeroed in on those deaths that required a mention of pregnancy among the causes on a death certificate.

• They found overall maternal deaths were stable, at just over 10 per 100,000 live births for the periods 1999 to 2002 and 2018 to 2021.
• In contrast, maternal death rates recorded by the Centers for Disease Control and Prevention, where NCHS is housed, rose from 9.65 per 100,000 to 23.6 per 100,000 for those periods.

Deaths resulting from obstetric causes such as hemorrhaging or preeclampsia decreased over those time periods, the study found.

• Meanwhile, deaths from indirect causes like hypertension that were aggravated by pregnancy rose.
• Non-Hispanic Black women still had disproportionately high rates of maternal death, with striking disparities due to ectopic pregnancy, cardiovascular conditions and kidney and other diseases.

What they're saying: "The CDC has acknowledged in the past that errors were artificially inflating numbers, but their efforts to correct those errors haven't worked," said Cande Ananth, chief of the division of epidemiology and biostatistics at Rutgers Robert Wood Johnson Medical School and senior author of the study.

Between the lines: The CDC changed the rules on the use of checkbox in 2018, limiting it to women age 15 to 44. But the system still counts many non-maternal and incidental deaths, such as those from a car accident, as maternal deaths, researchers said.

• Ananth said recent increases in the official numbers are also partly driven by the tendency to include more cancers unrelated to pregnancy in maternal death rates.

The other side: The CDC's most recent maternal death report for 2021 found an almost 40% jump in deaths over 2020, with rates for Black women 2.6 times higher than for white women.

• NCHS declined NPR's request for comment on the study.

What we're watching: Researchers said one way to improve the checkbox system of death identification would be requiring certifying physicians to specify the pregnancy-related cause of death.

• Their findings of a significantly higher non-maternal death rate from hypertension also point to the need for an increased focus on treating the condition in women of reproductive age.