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Contents: Original Research

Health Care Disparity and Pregnancy-Related Mortality in the United States, 2005–2014

Moaddab, Amirhossein MD; Dildy, Gary A. MD; Brown, Haywood L. MD; Bateni, Zhoobin H. MD; Belfort, Michael A. MD, PhD; Sangi-Haghpeykar, Haleh PhD; Clark, Steven L. MD

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doi: 10.1097/AOG.0000000000002534
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The United States ranks much higher in pregnancy-related mortality in comparison with most other developed countries.1 Of equal concern is the observation that this situation is not improving; U.S. maternal mortality ratios have remained stable for several decades and appear to be increasing.2,3 Within the United States, significant variation exists in maternal mortality ratios for individual states.3 Such differences could be the result of variations in funding, oversight, or organization of state health care services and could reflect the intrinsic quality of available health care. Alternately, this variation may simply be a product of differences in the prevalence of medical risk factors for poor perinatal outcomes or demographic disparities with lack of access to medical–obstetric services.4,5 We sought to update the available 2006–2010 national mortality report, to investigate factors associated with differential state maternal mortality ratios, and to quantitate the contribution of various demographic factors to such variation.

Fig. 1.
Fig. 1.:
Trends in maternal mortality ratio (maternal deaths/100,000 live births) by ethnic group and race: United States, 2005–2014. Numbers in parentheses represent P values for the Jonckheere-Terpstra test.Moaddab. Trends in Maternal Mortality: 2005–2014. Obstet Gynecol 2018.

MATERIALS AND METHODS

This was a retrospective, observational study. We used data from the National Vital Statistics System. The birth data are published by the Centers for Disease Control and Prevention's (CDC) National Center for Health Statistics and include all events occurring between 2005 and 2014 for all 50 states and the District of Columbia.6–16 Maternal demographic characteristics (age, marital status, education, state of residence, and race), lifestyle and health characteristics (tobacco use, previous cesarean delivery, prepregnancy diabetes, gestational diabetes, prepregnancy hypertension, pregnancy-induced hypertension, prepregnancy obesity [body mass index (calculated as weight (kg)/[height (m)]2) 25 or greater], and eclampsia), and medical service utilization (method of delivery, source of payment, and number of prenatal visits) were extracted from this same CDC database.16

Maternal death data are based on the Detailed Mortality-Underlying Cause of Death database (CDC WONDER) that contains mortality and population counts for all U.S. counties.17 These data are based on death certificates for U.S. residents. Each death certificate identifies a single underlying cause of death (four-digit International Classification of Diseases, 10th Revision [ICD-10] code) and associated demographic data. When more than one cause or condition was entered by the physician, the underlying cause was determined by the sequence of conditions specified on the certificate.17 Maternal causes are those assigned to categories A34, O00–O95, and O98–O99 of the ICD-10, Second Edition.18–20 The CDC WONDER data set terms of use do not permit republication of the publically available individual data from states with annual maternal deaths of nine or less.17 Therefore, neither the available individual mortality counts nor ratios derived from these counts for individual states are reproduced in this article.17 A maternal death is defined by the CDC as a death occurring during pregnancy or within 1 year of birth.

Data on urban makeup of the population, percentage of unintended pregnancies, health insurance coverage of women ages 15–49 years, and adult woman poverty rate were also collected.21,22 The number of missing values used in the final analysis was less than 1% of all data in aggregate; in terms of the data representing the primary focus of this study, only 22 of 7,031 (0.3%) total maternal deaths were not associated with a specific ethnic status.

We used publically available data that do not contain any individual identifiers; thus, this study was exempt from human subject research regulatory and institutional review board approval.

Bivariate correlations between maternal mortality ratio and all maternal demographic, lifestyle, health, and medical service utilization characteristics were calculated. We also performed a maximum likelihood factor analysis with varimax rotation retaining variables that were significant (P<.05) in the univariate analysis. Factor analysis was performed to deal with multicollinearity among the existing variables and to better identify variables that most closely and independently predicted maternal mortality ratio. We assessed the association between the extracted factors and maternal mortality ratio by correlation and regression analyses and used the Jouckheera-Terpska test to determine the presence or absence of a trend, either increasing or decreasing. A P value of <.05 was considered statistically significant. In all cases, ethnic designation is as reported in the original CDC data. All analyses were performed in SAS 9.4 and statistical software package SPSS 21.0.

RESULTS

Between 2005 and 2014, there were 40,922,512 live births and 7,031 maternal deaths in the United States (Tables 1 and 2). Table 3 details correlation coefficients between demographic, lifestyle, health, and socioeconomic characteristics and available maternal mortality ratio.17

Table 1.
Table 1.:
Number of Maternal Deaths and Live Births by Year and Age, United States, 2005–2014
Table 2.
Table 2.:
Maternal Mortality Ratio, Deaths per 100,000 Live Births by Age
Table 3.
Table 3.:
Correlation Coefficients Between State-Specific Maternal Demographic, Lifestyle, Health, and Socioeconomic Characteristics and Maternal Mortality in the United States, 2005–2014*

The overall mortality ratio during this period of time was 15.6 per 100,000. As demonstrated in Table 2 and Figure 1, after a slight decrease from 15 to 12 per 100,000 live births between 2005 and 2007, there has been a continued increase in maternal mortality ratio since 2007 with a rate of 21–22 per 100,000 live births in 2013 and 2014 (P<.001) This trend was most pronounced in women aged 45 years and older, although the numbers are small in this subgroup. As demonstrated in Figure 1, the recent increase in mortality was most pronounced in non-Hispanic black women and of lesser magnitude in Native American and non-Hispanic white women. This increase was not seen in Asian or Hispanic women after 2008. There was a significant correlation between state mortality ranking and the proportion of non-Hispanic black women in the delivery population and an inverse correlation with deliveries to non-Hispanic white women (Table 3). Of all risk factors examined (Table 3), only gestational diabetes, cesarean deliveries, unintended births, unmarried status, percentage of deliveries to non-Hispanic black women, and four or fewer prenatal visits were significantly (P<.05) associated with maternal mortality ratio. The probability level for the χ2 test was P>.05 for the hypothesis of one common factor, indicating the one-factor model was an adequate representation. Regarding these risk factors, factor, the highest correlation, based on standardized regression coefficients, was seen with the variable of deliveries to black women (0.39). Weaker regression coefficients included those for unmarried status and cesarean deliveries (0.25), unintended pregnancy (0.17), fewer than four prenatal visits (0.04), and diabetes (−0.05) This factor, which can be interpreted primarily as sociodemographic characteristics, had a correlation of 0.51 with maternal mortality ratio (P=01). The presence of both unmarried status and cesarean delivery on this factor is expected because black ethnicity had a high association with both unmarried status (r=0.65) and with cesarean delivery (r=0.66) (P<.001).

DISCUSSION

The U.S. maternal mortality ratio continues to climb and reached a rate of 21–22 per 100,000 in 2013 and 2014. Many explanations for this trend have been offered. Although the United States has a higher rural population than many European nations, Canada, a nation which is even more rural, has a maternal mortality ratio less than half of the United States'—10 per 100,000 live births.23 Furthermore, our data failed to identify a statistical correlation between state-specific maternal mortality and either rural status or poverty (Table 3). Immigration has also been cited as a factor in this mortality trend. However, we found lower mortality for Hispanic women who make up the majority of recent immigrants (Fig. 1). This finding has been noted previously and has been attributed to unique social factors and family support often available to these women.24

The high U.S. cesarean rate has also been invoked as an explanation for increased mortality, yet our data demonstrate only a weak correlation of mortality with cesarean delivery. Furthermore, previous work has demonstrated that this correlation does not reflect causation; the overwhelming majority of maternal deaths associated with cesarean delivery is a consequence of the indication for the cesarean delivery, not the operation itself.25 Although medical factors such as hypertensive disease, diabetes, tobacco use, and obesity have been shown to be correlated with increased maternal morbidity, statewide population differences in rates of these conditions were not significantly correlated with mortality ratios (Table 3). The 1999 change in maternal mortality coding practices (ICD-9 to ICD-10) could also be invoked as an explanation for this trend in the United States. However, the continued upward trend in mortality more than a decade later, and the absence of such a trend in Canada,23 which uses the same coding system, casts doubt on this assumption.

Our data suggest that much of the variation in statewide maternal mortality ratios in the United States is accounted for by social rather than medical or geographic factors: unintended pregnancy, unmarried mother, and non-Hispanic black race (Table 3). These data provide evidence for a strong contribution of racial disparity to maternal mortality ratio in the United States. Particularly striking is the close correlation between ethnic background and maternal mortality. A factor derived from factor analysis, which primarily represented ethnic background, accounted for 26% of the differences in statewide mortality. Excellent care is apparently available, but is not reaching all the people.

These data support two conclusions. First, although low state maternal mortality ratios may reflect state-specific excellence in quality, leadership, organization, and funding of obstetric health care, such favorable ranking could simply reflect a different proportion of non-Hispanic black patients in the population rather than intrinsically superior medical care. The converse applies as well.

Second, comparative health care statistics that do not adjust for these important demographic factors are of little significance in judging the intrinsic quality of available health care in an individual state or region. The potential relative contributions of factors such as racial disparities in health care availability and access or utilization by underserved populations are not addressed by our data, but are important issues faced by states seeking to decrease maternal mortality. Ethnic genetic differences may also be involved. In addition, the potential role of unconscious (implicit) bias in this significant racial disparity must be considered.25

Finally, available publications consistently document relatively good maternal outcomes for select groups of otherwise healthy older women undertaking pregnancy.26,27 Such data, coupled with the national age-related mortality ratios presented in Tables 1 and 2, suggest that many older mothers in the United States are not healthy. The mortality ratio in women 45 years of age or older surpasses those in many low-resource nations. Again, these numbers are small, suggesting caution in interpretation of these data. However, careful health screening and preconception counseling are recommended before recommending pregnancy to such women. This is particularly germane to women who plan to conceive after assisted reproductive technologies because in this population, such screening should always be possible.

This study has several limitations. First, it is recognized that significant underreporting of U.S. maternal mortality exists when data are obtained based on ICD cause-of-death codes.28 Actual maternal mortality rates are therefore likely to be higher than those reported here. In addition, our data sets do not allow a precise determination of the causes of death, although such data have been extensively reported in other recent series from the United States.29,30

We conclude that the increased mortality ratios seen in the United States in recent years reflect significant social as well as medical challenges and are closely related to lack of access to health care in the non-Hispanic black population. Our results provide evidence for the strong contribution of racial disparity to the maternal mortality ratio in the United States and suggest that addressing issues related to health care disparity and access for this population will play an important role in national attempts to reverse this mortality trend.

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© 2018 by American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.