Last July, PBS (and others) reported that the US was experiencing a maternal health crisis.

Maternal deaths across the U.S. more than doubled over the course of two decades, and the tragedy unfolded unequally.

Black mothers died at the nation’s highest rates, while the largest increases in deaths were found in American Indian and Native Alaskan mothers. And some states — and racial or ethnic groups within them – fared worse than others...

“It’s a call to action to all of us to understand the root causes — to understand that some of it is about health care and access to health care, but a lot of it is about structural racism and the policies and procedures and things that we have in place that may keep people from being healthy,” said Dr. Allison Bryant, one of the study’s authors and a senior medical director for health equity at Mass General Brigham.

The American Medical Association called the rise "alarming." But a new study says the rise in maternal mortality was actually a case of bad data. Using another way to measure the researchers found maternal mortality has basically been flat in the US for the past two decades.

Data classification errors have inflated U.S. maternal death rates for two decades, according to the study, published Wednesday in the American Journal of Obstetrics & Gynecology. Instead of the maternal death rate more than doubling since 2002, it has remained flat, researchers found.

“There has been a lot of alarm and apprehension surrounding the fact that some of these reports show a threefold increase in maternal mortality, and that is not what we found. We found low and stable rates,” said K.S. Joseph, the study’s lead author and professor in the departments of obstetrics and gynecology and the School of Population and Public Health at the University of British Columbia in Vancouver.

How does a mistake like this happen? It turns out to be the result of a check box that was added to death certificates 21 years ago.

In 2003, the National Vital Statistics System added a checkbox to death certificates to note whether the deceased person was pregnant or had recently been pregnant to address concerns that pregnancy-related deaths were being undercounted.

But the box was checked for many deaths that were unrelated to pregnancy or childbirth, researchers found. For example, hundreds of deaths of people 70 or older were mistakenly classified as having been pregnant. Deaths from cancer and other causes also were counted as maternal deaths if the box was checked. As a result, the maternal mortality rates showed a dramatic increase since 2003.

The purpose of the checkbox was to correct what many experts believed was an underestimate of the maternal death rate. But the fix wound up creating a vast overestimate. One state that took a different approach to collecting the data was Texas.

Texas has undertaken significant efforts to refine the data it collects on maternal mortality, developing a four-part “enhanced method” for identifying maternal deaths that has been in place for years.

The pregnancy checkbox has helped identify some maternal deaths that may have otherwise been missed, but it has also “proven to be open to error,” said Savannah Larimore, manager of maternal mortality and morbidity epidemiology with the Texas state health department.

Like the new study suggests, Texas has seen general stability in maternal mortality rates in recent years.

In fact, if you only look at the clear cases of maternal death related to delivering babies, that rate has dropped more than 50% over the last 12-13 years. It's the addition of all of these edge cases and errors that drove the numbers higher. Unfortunately, even with the corrections made to the data, it still shows big differences in maternal mortality between different races.

Researchers noted that gaping racial disparities remain — especially between White and Black pregnant people. Black pregnant people die at nearly three times the rate of their White peers because they face higher rates of pregnancy complications such as ectopic pregnancy and eclampsia, as well as chronic diseases such as high blood pressure, heart disease and kidney failure, researchers found.

Overall the revised US rate of maternal mortality is slightly higher than the UK but much higher than some other countries in Europe.