Is the United States Maternal Mortality Rate Increasing? Disentangling trends from measurement issues Short title: U.S. Maternal Mortality Trends

Introduction

Maternal mortality is an important indicator of the quality of health care both nationally and internationally (1–3). The death of a mother during pregnancy, childbirth or post-partum is one of the greatest tragedies that can occur within a family, with wide-ranging consequences for the index child, other children, spouses, other family members, and the larger society (1–5).

The Centers for Disease Control and Prevention’s National Center for Health Statistics (NCHS) is the source of official United States’ maternal mortality statistics used for both sub-national and international comparisons (6). Studies based on data from the 1980s and 1990s identified significant underreporting of maternal deaths in the National Vital Statistics System (7–8). To improve ascertainment, a pregnancy question was added to the 2003 revision of the U.S. standard death certificate. The question has several checkboxes to ascertain whether female decedents were: Not pregnant within past year; pregnant at time of death; not pregnant, but pregnant within 42 days of death; not pregnant, but pregnant 43 days to 1 year before death; or unknown if pregnant within the past year (9). The use of this pregnancy question has improved ascertainment of maternal deaths, and led to increases in reported maternal mortality rates (6).

However, there were delays in states’ adoption of the revised death certificate, and thus the new pregnancy question (6, 10, 11). In addition, some states had pregnancy questions that were inconsistent with the U.S. standard (6). This created a situation where, in any given data year, some states were using the U.S. standard question, others were using questions incompatible with the U.S. standard, and still others had no pregnancy question on their death certificates (6, 10, 11).

Due in part to the difficulties in disentangling these effects, the United States has not published an official maternal mortality rate since 2007 (11). This has led to a deficit of information both nationally and internationally, at a time when greater attention has been focused on maternal mortality than ever before (1–5, 12–13). For example, United Nations’ Millennium Development Goal 5a was to reduce the maternal mortality rate by 75% between 1990 and 2015 (12).

A supplemental data system, the Pregnancy Mortality Surveillance System, collects data on pregnancy-related deaths (within 1 year of pregnancy), and has found recent increases in these deaths (14–15). However, since this system is based in large part on official vital statistics data (together with supplementary reports), these data could also have been influenced by the improved ascertainment of maternal deaths in the National Vital Statistics System. Thus, there is currently no clear picture of maternal mortality trends in the U.S. The aims of this study were to: 1) develop and test methods for trend analysis of vital statistics maternal mortality data from 2000–2014, taking into account state revision dates and different question formats; and 2) provide an overview of trends in U.S. maternal mortality rates from 2000–2014.

Methods

The World Health Organization defines maternal death as: “The death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the duration and the site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management, but not from accidental or incidental causes” (16). This is the definition used for international maternal mortality comparisons. The WHO also provides a separate definition for late maternal deaths: “The death of a woman from direct or indirect obstetric causes more than 42 days but less than one year after termination of pregnancy” (16).

United States maternal mortality data used for national and international comparisons are based on information reported on death certificates filed in state vital statistics offices, and subsequently compiled into national data through the National Vital Statistics System (10–11). Physicians, medical examiners or coroners are responsible for completing the medical portion of the death certificate, including the cause of death. From 1999 to the present, cause-of-death data in the United States have been coded according to the International Statistical Classification of Diseases and Related Health Problems, 10^th Revision (ICD-10) (10–11). Maternal deaths are denoted by ICD-10 codes A34, O00–O95, O98–O99, while late maternal deaths are denoted by ICD-10 codes O96–O97 (6).

Maternal mortality data used in this study were derived from the detailed mortality data files publically available from NCHS, and also available through CDC-WONDER (17–18). Maternal mortality rates were computed per 100,000 live births. Joinpoint regression analysis was used to model trends over time (19). This approach is also commonly referred to as piecewise or segmented regression and has been implemented to test for differences in adjacent time trends using permutation tests and assessing overall model fit using the Bayesian Information Criterion (19). Because the study was based on de-identified, aggregated data from U.S. government public-use data sets, the study was exempt from requiring institutional review board approval.

Results

Simply totaling the raw, unadjusted data from all states regardless of whether or not they revised their death certificates results in a reported U.S. maternal mortality rate that more than doubled from 9.8 maternal deaths per 100,000 live births in 2000 to 21.5 in 2014 (17). However, the adjusted maternal mortality rate increased more slowly for a group of 24 states and Washington D.C. (Analysis Group 1 – see Table 1) that only included a pregnancy question after they revised their death certificates (Figure 1). The correction factor for Group 1 states was 1.932 (483 maternal deaths in the two years after revision/250 maternal deaths in the two years prior to revision). The modeled adjusted maternal mortality rate for Group 1 states, which adjusts for presumed undercounting in the years prior to revision, increased from 18.2 in 2000 to 22.8 in 2014. The slope of the regression line was 0.33 (95% CI 0.07, 0.58), and was based on 3,108 maternal deaths and 19,328,481 live births from 2000–2014.

Group 2 included states that had a non-standard pregnancy question prior to revision, and revised to the U.S. standard. The correction factor for these states was 2.067 (676/327 maternal deaths). Among these states, the adjusted maternal mortality rate was higher than reported in 2000 (18.4) and rose to 24.5 in 2014. The slope of the regression line was 0.44 (95% CI 0.05–0.82) (based on 3,098 maternal deaths and 18,136,263 births) (Figure 2).

Data for Analysis Groups 3 (8 states) and 4 (3 states) are analyzed without adjustment and are shown in Figure 3. For Group 3, states that did not revise and did not have a comparable question pre-revision, the rates reported are uniformly lower than for other states and the modeled maternal mortality rate was 8.0 in 2000 and increased to 10.4 in 2013. The slope of the regression line was 0.19 (95% CI −0.02, 0.39) (638 maternal deaths and 6,804,191 live births). For Analysis Group 4, states that already had a comparable pregnancy question on their death certificate throughout the study period, the modeled maternal mortality rate rose from 14.0 in 2000 to 19.9 in 2014. The slope of the regression line was 0.42 (95% CI 0.09, 0.75), (425 maternal deaths and 2,453,198 live births).

California and Texas were analyzed separately as they had trends that were markedly different from other U.S. states, and sufficient numbers of maternal deaths for reliable trend analysis. Texas had an unrevised question about pregnancies in the past 12 months, and revised to the U.S. standard question in 2006. Adjusted maternal mortality rates for Texas show only a modest increase from 2000–2010, from a rate of 17.7 in 2000 to 18.6 in 2010. The slope of this regression line was 0.12 (95% CI −0.22, 0.46), (564 maternal deaths and 4,246,835 live births) (Figure 4). However, after 2010, the reported maternal mortality rate for Texas doubled within a two year period to levels not seen in other U.S. states. Joinpoint trend analysis was done separately for the 2000–2010 and the 2011–2014 periods as the trends for these two periods differed widely.

California data are shown in Figure 5 for maternal and late maternal deaths combined (those occurring within 1 year of pregnancy). The California rate was markedly lower in 2000–2002, before the pregnancy question was adopted, and the reported rate nearly doubled once the pregnancy question (asking about pregnancies <1 year) was introduced in 2003. As the 2000–2002 data were clearly not comparable, joinpoint regression analysis was done for the 2003–2014 data. The modeled maternal mortality rates decreased from 21.5 in 2003 to 15.1 in 2014. The slope of the line was −0.58 (95% CI −1.05, −0.11), or 0.58 unit of decrease in the combined maternal and late maternal mortality rate per year (based on 1,190 maternal deaths and 6,356,032 live births).

Finally, we provide estimated maternal mortality rates for 48 states and DC from 2000–2014 (Table 2). For the 48 states and D.C. (excluding California and Texas), the estimated maternal mortality rate in 2000 was 18.8, and the rate increased slowly to a rate of 23.8 in 2014, an increase of 26.6% (Table 2). The slope of the regression line was 0.36 (95% CI 0.05, 0.67), based on 7,269 reported maternal deaths and 46,722,133 live births from 2000–2014. Since the reported (unadjusted) maternal mortality rate for the 48 states and DC increased by 132.3% from 2000–2014 (from 9.9 to 23.0) (17), we estimate that 20.1% (26.6%/132.3%) of the observed increase in the maternal mortality rate from 2000–2014 was due to a real increase in maternal mortality, and 79.9% was due to improved ascertainment.

Discussion

Despite the United Nations Millennium Development Goal for a 75% reduction in maternal mortality from 1990–2015 the reported (unadjusted) U.S. maternal mortality rate more than doubled from 2000–2014. As we’ve shown, most of the reported increase in maternal mortality rates from 2000–2014 was due to improved ascertainment of maternal deaths. However, combined data for 48 states and DC showed an increase in the estimated maternal mortality rate from 18.8 in 2000 to 23.8 in 2014 - a 26.6% increase. Notably, the smaller increase seen in the adjusted data appears to be a result of earlier estimates of the U.S. national rate being substantially underreported. Clearly at a time when WHO reports that 157 of 183 countries studied had decreases in maternal mortality between 2000 and 2013 (21), the U.S. maternal mortality rate is moving in the wrong direction. Among 31 Organization for Economic Cooperation and Development (OECD) countries reporting maternal mortality data, the U.S. would rank 30^th, ahead of only Mexico (22).

California, however, showed a marked decline in maternal and late maternal mortality from 2003–2014. California has made concerted efforts to reduce maternal mortality, including initiating a statewide pregnancy-associated mortality review in 2006, and contracting with the California Maternal Quality Care Collaborative to investigate primary causes of maternal death. This collaborative developed and promulgated evidence-based tool kits to address two of the most common, preventable contributors to maternal death (obstetric hemorrhage and preeclampsia), and implemented quality improvement initiatives throughout the state (23–25). These efforts appear to have helped reduce maternal mortality in California (23).

The Texas data are puzzling in that they show a modest increase in maternal mortality from 2000–2010 (slope=0.12) followed by a doubling within a 2-year period in the reported maternal mortality rate. In 2006, Texas revised its death certificate, including the addition of the U.S. standard pregnancy question, and also implemented an electronic death certificate. However, the 2006 changes did not appreciably affect the maternal mortality trend after adjustment, and the doubling in the rate occurred in 2011–2012. Texas cause-of-death data, as with data for most states, are coded at NCHS, and this doubling in the rate was not found for other states. Communications with vital statistics personnel in Texas and at NCHS did not identify any data processing or coding changes that would account for this rapid increase. There were some changes in the provision of women’s health services in Texas from 2011–2015, including the closing of several women’s health clinics (26–27). Still, in the absence of war, natural disaster, or severe economic upheaval, the doubling of a mortality rate within a 2-year period in a state with almost 400,000 annual births seems unlikely. A future paper will examine Texas data by race/ethnicity and detailed causes of death to better understand this unusual finding.

The larger correction factor for Group 2 than for Group 1 states is not surprising when examined in the context of NCHS coding rules. These rules code pregnancy data for states with a pregnancy question with a timeframe longer than the 42 day standard to late maternal death (O96–97) codes, which are by definition excluded from standard maternal mortality calculations (6). This decision is understandable as the more conservative approach, since the exact timing of death was unknown. However, it has caused significant disruption in trend analysis of maternal and late maternal mortality rates. This is because most maternal deaths within 1 year of pregnancy actually occur during or very soon after pregnancy. For example, in 2009 (about the mid-point in the adoption of the revised certificate) 64% of maternal deaths <1 year were coded to the late maternal (O96–O97) category for the 8 unrevised states that had a pregnancy question with a timeframe longer than the 42-day standard, compared to just 21% for the 30 revised states that had adopted the U.S. standard pregnancy question.

The strengths of the study include the use of vital statistics data that provide information on all births and deaths in the United States during the study period. The limitations of the study are also those of vital statistics, and include concerns about the accuracy of cause-of-death information provided by the physician, medical examiner or coroner (7, 28). The prompt nature of vital statistics registration also means that such registration may initially occur based on an interim cause of death, which, depending on the efficiency of state systems, may or may not be updated after cause-of-death investigations are completed (29). Evaluation of the accuracy of reporting of the pregnancy question is important as this information is used in conjunction with the reported causes of death to classify maternal deaths (28). However, the pregnancy data are currently not included on public-use data sets (17–18), so such evaluations are infeasible for non-NCHS researchers. During the time period under study, states have increasingly moved towards electronic death registration, and away from paper-based death certificates. NCHS has continued to provide training in cause-of-death certification to state vital statistics personnel and has recently taken on a greater role in coding cause-of-death data. However these changes are unlikely to have substantially influenced maternal mortality reporting (20).

It is an international embarrassment that the United States, since 2007, has not been able to provide a national maternal mortality rate to international data repositories such as those run by the OECD (22). This inability reflects the chronic underfunding over the past two decades of state and national vital statistics systems. Indeed, it was primarily a lack of funds that led to delays (of more than a decade in many states) in the adoption of the 2003 revised birth and death certificates. And this delay created the complex data comparability problem addressed in this study. The lack of publication of U.S. maternal mortality data since 2007 has also meant that these data have received a lesser degree of scrutiny and quality control, when compared to published vital statistics measures such as infant mortality. For example, had NCHS and the Texas vital statistics office both been publishing annual maternal mortality rates, the unusual findings from Texas for 2011–2014 would certainly have been investigated much sooner and in greater detail. Accurate measurement of maternal mortality is an essential first step in prevention efforts, as it can identify at-risk populations and measure the progress of prevention programs.

In conclusion, the maternal mortality rate for 48 states and Washington D.C. from 2000–2014 was higher than previously reported, is increasing, and places the U.S. far behind other industrialized nations. There is a need to redouble efforts to prevent maternal deaths and improve maternity care for the 4 million U.S. women giving birth each year.