There is no charity walk to raise awareness about the 700 to 800 women that die each year during pregnancy or shortly after giving birth in the U.S. There are no dedicated colored-plastic wristbands. But statistics in recent years have revealed a worrisome trend: the rate of maternal mortality in the U.S. has more than doubled in the past few decades. Whereas 7.2 women died per 100,000 births in 1987, that number swelled to 17.8 deaths per 100,000 live births in 2009 and 2011. The uptick occurred even as maternal mortality dropped in less-developed settings around the world. Now women giving birth in the U.S. are at a higher risk of dying than those giving birth in China or Saudi Arabia. The reason for this disturbing trend has eluded researchers, however.

So what exactly is it about being in a family way that is getting worse in America? According to some experts at the U.S. Centers for Disease Control and Prevention (CDC), perhaps nothing. A deeper dive into the mortality data and the conditions under which they were collected suggests that the apparent doubling may not necessarily mean that more mothers are dying than ever before. Instead, administrative issues in the past may have camouflaged a problem that is only now coming to light.

Statistics for 40 states and the District of Columbia, gleaned from death certificates, indicate that whereas the reported maternal mortality rate from 1999 to 2002 was 9.8 per 100,000 live births, it jumped to 20.8 per 100,000 live births for the period 2010 to 2013. But the numbers in the latter period may have been affected by a small change in the forms that are filed when a person dies. Until relatively recently most states relied on a death certificate form that was created in 1989. A newer version of the form, released in 2003, added a dedicated question asking whether the person who died was currently or recently pregnant—effectively creating a flag for capturing maternal mortality. Specifically, this recently introduced question asks if the woman was pregnant within the past year, at the time of death or within 42 days of death.

The addition of this question means that the apparent increase in maternal mortality in the U.S. “is almost certainly not a real increase. It’s better detection from the new certificates,” says Robert Anderson, chief of the Mortality Statistics Branch with the CDC’s National Center for Health Statistics. “The numbers are going up but it’s most likely not because women are more likely to die,” he contends. (Anderson’s branch of CDC counts maternal mortality as death during pregnancy or in the following 42 days; some other researchers look at the whole year after giving birth.) States have been slow to switch over to the new form and even now two states—Alabama and West Virginia—still have not adopted it. But “as the certificate with the check box is being implemented over time, we are detecting more maternal deaths,” Anderson says. Another administrative change in how deaths were classified and coded internationally, called the International Statistical Classification of Diseases and Related Health Problems, 10th Edition (ICD-10), is also widely believed to be a contributing factor to the uptick in death numbers.

Yet there may be more to the maternal mortality increase than better detection of an existing problem. Nicholas Kassebaum, a professor of anesthesiology and pain medicine at the University of Washington, has led an independent analysis looking at ICD-9 and ICD-10 coding and maternal mortality, and says that it is very unlikely the rise in deaths comes merely from administrative shifts like transitioning to the new ICD or introducing a check box. “I can’t completely rule out that there is some effect from changing in coding on the magnitude of maternal mortality,” Kassebaum says, but it’s likely a “small effect.” His team looks at all deaths—not just maternal mortality—so if those deaths had been misclassified elsewhere, they likely would have picked them up and seen a large shift in those numbers following the ICD and check-box transitions, he says.

U.S. maternal mortality rates continue to climb even as other developed countries improve.

A worrisome trend, undetected

Still, even if the newer death toll numbers are just more accurately representing the number of women who die due to complications during pregnancy and childbirth, it’s a large number that demands explanation. Certainly, childbirth becomes more dangerous when a woman is not healthy before she becomes pregnant, and a growing body of research suggests that poor health prior to pregnancy could be a contributing factor to the high U.S. death toll. Many studies have indicated that an increasing number of pregnant women in the U.S. have health conditions that could boost the risk of problematic complications including chronic health disease, hypertension and diabetes. More than half of the women in the U.S. who become pregnant are above a healthy weight. Women who are 35 or older are also at increased risk of complications during pregnancy. Poor prenatal care and barriers to accessing health care could be killing more women, too.

Inadequate postnatal care may be another driver of mortality in women—one that that doesn’t show up in the official U.S. data analysis by the National Center for Health Statistics because the deaths tend to occur more than 43 days after pregnancy ends. “We are good at responding to life-threatening crisis that may have killed women a generation ago,” Kassebaum observes. But, he notes, poor postnatal care in women who were significantly weakened by childbirth complications may be killing more women.

Why are more women dying between 43 days and a year after the end of pregnancy?

Racial Divide

One aspect of maternal mortality that has not changed over the years is the extent to which it varies by race. The risk of maternal mortality has remained about three to four times higher among black women than white women during the past six decades. Since 1999 maternal mortality has climbed among both black and white women—potentially due to those changes in death certificates and also how deaths are now coded in the U.S. using the ICD-10. Yet even with the cross-race increases in deaths related to pregnancy, in 2007 the maternal mortality rate for black women was still nearly three times higher than the rate for white women.

Maternal mortality rates for black women in the U.S. are roughly three times higher than the rate for white women.

Researchers have shown that black women are not inherently more likely to have underlying pregnancy complications. Indeed, one national study that looked at five major common causes of maternal death and injury that collectively account for more than a quarter of all pregnancy-related deaths found that black women did not have a significantly higher prevalence than white women of those conditions—preeclampsia, eclampsia, obstetric hemorrhage, placental abruption and placenta previa. Yet black women were two to three times more likely to die than white women with the same complication.

For now, more interventions to keep women healthier even before they get pregnant, better care during and after pregnancy and better tracking of maternal deaths will be essential tools in the fight to save women from these preventable deaths.