Maternal Mortality Increase Explained by Coding Changes?

Tara Haelle

December 13, 2016

The maternal mortality rate in the United States has climbed — or appeared to have climbed — during the last decade to such an extent that by 2013, it surpassed the rates in Iran, Kazakhstan, Libya, Uruguay, and other countries. Although researchers have proposed chronic disease, including obesity, and increased rates of cesarean delivery as potential contributors to the increase, the true explanation may lay in surveillance improvements and changes in coding of maternal deaths, according to a study published online December 2 and in the January 2017 issue of Obstetrics & Gynecology.

Maternal deaths include those occurring during pregnancy or within 42 days of a pregnancy that are directly caused by pregnancy or its management, according to the World Health Organization. (The US Pregnancy Mortality Surveillance System tracks deaths up to 1 year after pregnancy, but those are coded as late maternal deaths and included in different statistics.)

However, "identification of maternal deaths can pose a challenge because recent or current pregnancy may remain unrecognized," write K. S. Joseph, MD, PhD, from the University of British Columbia in Vancouver, Canada, and colleagues. "For instance, the underlying cause of death for a woman who experiences acute renal failure as a result of pregnancy complications and dies 5 weeks after delivery may be listed as acute renal failure (and not identified as a maternal death)," they write.

Additional challenges include the difficulty of determining causation if insufficient information is available regarding pregnancy complications, clinical factors, prenatal care status, live birth order, and pregnancy outcome, which is commonly the case. Even if those could be overcome, however, it was not until the introduction of the International Classification of Diseases, 10th Revision (ICD-10), that it was even possible to code for both maternal status and a condition that may not necessarily appear pregnancy-related. The ICD-10 added more conditions under the O classification.

Dr Joseph and colleagues therefore retrospectively analyzed data from the Centers for Disease Control and Prevention on maternal deaths and live births in the United States between 1993 and 2014 to determine what role the ICD revisions had on mortality rates. They used ICD-9 codes to identify causes of death up until 1998 and ICD-10 codes for 1999 and 2014 before calculating maternal mortality rate ratios (RRs) for all years.

Among 4,000,240 live births in the United States in 1993, maternal deaths numbered 302, translating to a maternal mortality ratio of 7.55 deaths per 100,000 live births that year. The maternal mortality ratios increased to 9.88 per 100,000 births in 1999 and 21.5 per 100,000 births in 2014, making the 2014 ratio estimate nearly three times greater than the ratio 2 decades earlier (RR, 2.84; 95% confidence interval [CI], 2.49 - 3.24).

Similarly, compared with 1999, the 2014 ratio estimate more than doubled (RR, 2.17; 95% CI, 1.93 - 2.45).

Yet, when the researchers looked at more details, the data were not consistent. During the same period, 1999 to 2014, maternal deaths from complications of labor and delivery actually decreased (RR, 0.43; 95% CI, 0.27 - 0.68). Further, maternal deaths from "abortive outcomes (O00–O07), edema, proteinuria and hypertensive disorders (O10–O16), maternal care related to the fetus and amniotic cavity (O30–O48), and complications predominantly related to the puerperium" did not significantly change between 1999 and 2014. Instead, dramatic increases during this time occurred for "deaths resulting from other maternal disorders predominantly related to pregnancy (O20–O29) and deaths resulting from other obstetric problems not elsewhere classified (O95, O98, and O99)."

More specifically, maternal deaths from diabetes mellitus, liver disorders, renal disease, circulatory system diseases, and other diseases complicated by pregnancy or childbirth all increased 4 to 23 times, depending on the ICD-10 code, at the same time that deaths dropped (significantly) threefold for preeclampsia and eclampsia and (nonsignificantly) 36% for antepartum and postpartum hemorrhage.

The authors, therefore, say those maternal deaths that increased as a result of diabetes, liver disorders, and other conditions are responsible for the increase in overall maternal mortality, but they do not represent a real increase.

Rather, the addition of two ICD-10 codes enabled providers to code both for the specific condition and for maternal status. ICD-9 codes referred to specific conditions regardless of maternal status. It was the addition of these two ICD-10 codes, along with their use via improved surveillance methods, that accounts for the large increase in maternal mortality: O26.8 for "other specified pregnancy-related conditions" and O99 for "other maternal diseases classifiable elsewhere but complicating pregnancy, childbirth, and the puerperium." Although O26.8 covers a number of different conditions, renal disease is the condition likely responsible for most deaths under that code, Dr Joseph told Medscape Medical News.

When the researchers removed deaths classified with O26.8 and O99 from the maternal mortality calculations, the rate increase disappeared, leaving a rate ratio of 1.09 (95% CI, 0.94 - 1.27) for 2014 compared with 1999.

These codes, however, were introduced in 1999, so in theory, the increase in mortality should have been seen between 1998 and 1999. Instead, the increase happened incrementally as a result of several changes and improvements in surveillance. It was the combination of ICD-10 codes and surveillance methods that used them that together led to the perceived increase in maternal mortality, according to the authors.

"When these codes first went into use, we were still not able to find the deaths that fit the description of O26.8 and O99," Dr Joseph told Medscape Medical News. What changed was the addition of a checkbox asking about pregnancy on death certificates that various states implemented starting in 2003.

"Every time a woman dies, when you fill out the death certificate, you are forced to answer the question, 'Was this person pregnant in the last 42 days?'" Dr Joseph explained. "And now, if you tick yes to that box, it will get classified as a maternal death."

Several other changes to surveillance contributed to the increase in maternal mortality, the researchers found. One that occurred gradually throughout the 1990s was the addition of a separate question about pregnancy on death certificates before the checkbox was introduced. Another, thanks to full maturation of the information age, was the linkage of population birth records and death records so that it is easier to see which women gave birth within the previous year.

Adjustment for these surveillance changes yielded a maternal mortality rate of 8 per 100,000 live births in 2013 (RR, 1.06 compared with 1993; 95% CI, 0.90 - 1.25). (The researchers used 2013 instead of 2014 because the rates for those 2 years was so similar that the analysis could not distinguish between them, necessitating the use of 2013, Dr Joseph explained.)

Despite these explanations, the fact remains that on paper, the US maternal mortality rate exceeds those of many other countries throughout the world, including those mentioned at the start. The reason, Dr Joseph said, is that US surveillance is superior to that of most other places.

"Those countries have much, much worse systems of vital statistics and registration," Dr Joseph said. "In my opinion, they would have incomplete data on maternal deaths, which are very challenging to identify."

In fact, Canada also saw an increase in maternal mortality after the introduction of ICD-10 because the ICD-10 is much better at classifying maternal death, Dr Joseph said. The rate in Canada doubled, but the increase was not as dramatic as that in the United Sates because the checkbox on Canadian death certificates is not as standardized and consistently used as in the United States, he said.

Although these findings strongly suggest the bulk of maternal mortality increase has resulted from changes in surveillance and coding, researchers are still piecing together the full story, said Nancy C. Chescheir MD, editor-in-chief of Obstetrics & Gynecology and a professor of maternal-fetal medicine at the University of North Carolina School of Medicine in Chapel Hill.

"These findings certainly soften perhaps a little of the concern about change in the actual true mortality, but I don't think it's the whole story," Dr Chescheir told Medscape Medical News. "There are too many other articles and too much other research that tell a different story. What this article does is reinforce how complicated it is, but it doesn't wrap it up with a bow."

Together, the study findings should be reassuring, the authors suggest.

"Reports of temporal increases in maternal mortality rates in the United States have led to shock and soul-searching by clinicians," they write. "In fact, maternal deaths from conditions historically associated with high case-fatality rates including preeclampsia, eclampsia, complications of labor and delivery, antepartum and postpartum hemorrhage, and abortion either declined substantially or remained stable between 1999 and 2014."

Yet, they add, "Nevertheless, maternal mortality and especially severe maternal morbidity from such causes remain issues of serious concern and the routine clinical audit of such cases needs serious consideration."

Further, they note that some increases in maternal mortality may be occurring as a result of the increased use of assisted reproduction in older women and in women with chronic disease, even though these increases do not explain the twofold and threefold increases seen in official statistics.

"Although there may have been some increase in maternal deaths resulting from chronic diseases (such as diseases of the circulatory system, diabetes, and liver disease) and definite reductions in maternal death resulting from obstetric causes (such as preeclampsia, eclampsia, and complications of labor and delivery)," the authors conclude, "the overall picture is not consistent with any serious deterioration in maternal health or maternal health services in the United States."

Such pronouncements may run the risk of inducing some complacency, however.

"Even if this downgrades the absolute amount of maternal mortality, there's still too much," Dr Chescheir said. "I really, really hope this doesn't lead to complacency, but I'm a little concerned it might. It's always much nicer to hear you're doing something well than to hear that there may be a problem."

She does not expect these findings will change any clinical practice, however. Their implications are more likely to have an effect in the public health sphere.

"The doctor or midwife in practice taking care of a sick woman or a woman with risk factors for dying or who is acutely unstable is still going to take care of that patient," Dr Chescheir said. "I think the important thing is to realize is that these narratives will all fit together to give us the so-called truth. I think anyone going forward has to deal with this particular issue as they build the next phase of the story."

The research was funded through awards from the Canadian Institutes of Health Research, the British Columbia Children's Hospital Research Institute and a Vanier Canada Graduate Scholarship. The authors have disclosed no relevant financial relationships.

Obstet Gynecol. 2017;129:91-100. Abstract

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