Is maternal mortality in the U.S. on the rise, or are we just seeing more of it?

The maternal mortality rate in the U.S. has dropped drastically in the past hundred years – from an estimated 850 deaths/100,000 live births in 1900 to 7.2/100,000 in 1982. However, in recent years this trend has reversed itself, and maternal mortality in 2006 stood at 13.3/100,000 live births (Heron et al. 2006). Looking at these numbers, one can make the argument that it is becoming less and less safe to become pregnant in the U.S.

But where are those numbers coming from, and what are they really telling us? First, it is important to examine how data are collected and the changes that have taken place in maternal mortality reporting. Recognizing that maternal deaths have been historically underreported, many U.S. states have begun adding specific questions about pregnancy status on death certificates, meant to better identify deaths that occur in women who have been pregnant at any time in the past year.

Berg et al. (2003) concluded that increased maternal mortality rates from 1991-1997 were attributable to improved reporting:

The increase in the reported pregnancy-related mortality ratio from 1991 through 1997 almost certainly reflects improved ascertainment of pregnancy-related deaths. Beginning in 1991, the Division of Reproductive Health at the Centers for Disease Control and Prevention requested that states send to the Pregnancy Mortality Surveillance System all certificates for deaths occurring during or within 1 year of pregnancy, not just those which were coded as having been caused by pregnancy complications. At that time, the death certificates for 16 states and New York City contained check boxes or questions asking if the decedent had been pregnant at the time of death or within varying lengths of time before death. In addition, during the 1990s, many state health departments began to use computers to link death certificates of women of reproductive age to birth and fetal death certificates. This linkage and the presence of pregnancy check boxes on the death certificates allowed states to identify more deaths with a temporal relationship to pregnancy, from which those that were pregnancy related (ie, also causally related to pregnancy) could be found. This is reflected in the fact that the percent of the death certificates sent by state health departments to the Pregnancy Mortality Surveillance System that were determined, upon review, to be pregnancy related decreased from 97% for the years 1979–1986 7 to 89.9% for 1987–1990 8 to 59.9% for the period of the current report.

Horon (2005) explains the changes in reporting that took place due to changes in the International Classification of Disease definition of maternal mortality:

Changes were made in the classification of maternal deaths between ICD-9 and ICD-10. ICD-9 classified a death as having a maternal cause only if pregnancy was reported as part of the sequence of events leading to death. These deaths are classified as maternal in ICD-10 as well. However, the coding rules for ICD-10, unlike the rules for ICD-9, classify deaths aggravated by pregnancy as maternal deaths. This includes deaths from previously existing diseases and deaths from nonobstetric conditions that developed during pregnancy and were aggravated by physiological effects of pregnancy

All states had transitioned to using ICD-10 codes by 1999.

Hoyert (2007) concluded that increases from 1998 to 1999, and 2002 to 2003, were solely due to changes in coding and improved reporting, respectively:

In the NVSS [National Vital Statistics System], maternal deaths increased with the introduction of the ICD–10 and when the separate pregnancy status question switched from being supplemental information available from some state certificates to an item expected to be included on all state certificates. Maternal mortality rates increased for both of the years when these changes affecting identification of maternal deaths were implemented. Changes with the ICD–10 that resulted in more indirect maternal causes apply more with the increasing use of separate pregnancy questions. Because most states have yet to adopt the standard format of the separate pregnancy question, it is likely that maternal and late maternal death rates in all states will continue to be subject to increases because of the adoption of questions rather than actual increases in maternal mortality. The "pregnancy­ related mortality rates" using surveillance data increased between 1991 and 1999 (18). The increase in the surveillance data was attributed in large part to improved identification of "pregnancy-related deaths".

These changes in coding and reporting are necessary: more accurate count of pregnancy-related deaths is vital to efforts to combat maternal mortality. However, when looking at maternal mortality trends, keep in mind that these changes in reporting may be affecting our ability to directly examine pregnancy-related mortality trends over the past 15 years.

This is one of the issues being argued in California, which has seen a jump in maternal mortality, to 16.9/100,000 in 2006. This article on the increase presents several perspectives:

In 2007, the U.S. Centers for Disease Control and Prevention reported that the national maternal mortality rate had risen, but experts such as Dr. Jeffrey C. King, who leads a special inquiry into maternal mortality for the American College of Obstetricians and Gynecologists, chalked up the change to better counting of deaths. His opinion hasn’t changed.

“I would be surprised if there was a significant increase of maternal deaths,” said King, who has not seen the California report.

But Shabbir Ahmad, a scientist in California’s Department of Public Health, decided to look closer. He organized academics, state researchers and hospitals to conduct a systematic review of every maternal death in California. It’s the largest state review ever conducted. The group’s initial findings provide the first strong evidence that there is a true increase in deaths – not just the number of reported deaths. ...

The best estimates show that less than 30 percent of the increase is attributable to better reporting on death certificates. Even accounting for these reporting and classification changes, the maternal death rate between 1996 and 2006 has more than doubled, Main said.

Why has California not released their report on the rise maternal mortality so more people can examine the data directly? I wonder if they're still searching for an explanation in the reporting. When I was interning at a county health department last summer, new numbers came in on infant mortality that showed a surprisingly large increase on several measures. One of my fellow interns researched the change and discovered that it was produced by a change in reporting, and that other counties and states had reported the same phenomenon. Another project we were working on showed up with an error in the code that had underreported late preterm birth rates for years. It looks like the best investigatory efforts of public health professionals in California haven't revealed any such explanation, but (giving them the benefit of the doubt that they aren't just trying to suppress really bad numbers) they may still be hoping to explain away some of this data.

The bottom line with all of this is that while reporting changes may make it hard to make definitive statements about maternal mortality trends in the U.S., they are making it easier to make definitive statements about the current status of maternal mortality by revealing previously uncounted deaths. And the picture isn't pretty, most particularly from a health disparities perspective. While white women had an MMR of 9.5/100,000 in 2006, black women had an MMR of 32.7. In the California data, black women had an MMR of 54.9/100,000. If this is the real picture of maternal mortality in the U.S., we have a long, long way to go.


References

Berg, C. J., Chang, J., Callaghan, W. M., & Whitehead, S. J. (2003). Pregnancy-related mortality in the united states, 1991-1997. Obstetrics & Gynecology, 101(2), 289.

Heron, M., Hoyert, D. L., Murphy, S. L., Xu, J., Kochanek, K. D., & Tejada-Vera, B. (2009). Deaths: Final data for 2006. National Vital Statistics Reports : From the Centers for Disease Control and Prevention, National Center for Health Statistics, National Vital Statistics System, 57(14), 1-134.

Horon, I. L. (2005). Underreporting of maternal deaths on death certificates and the magnitude of the problem of maternal mortality. American Journal of Public Health, 95(3), 478.

Hoyert, D. L. (2007). Maternal mortality and related concepts. Vital & Health Statistics.Series 3, Analytical and Epidemiological Studies / [U.S.Dept.of Health and Human Services, Public Health Service, National Center for Health Statistics], (33)(33), 1-13.