Rural-Urban Differences in Maternal Mortality Trends in the United States, 1999–2017

Accounting for the Impact of the Pregnancy Status Checkbox

Lauren M. Rossen; Katherine A. Ahrens; Lindsay S. Womack; Sayeedha F. G. Uddin; Amy M. Branum

Disclosures

Am J Epidemiol. 2022;191(6) 

In This Article

Abstract and Introduction

Abstract

It has been difficult to measure rural-urban differences in maternal mortality ratios (MMRs) in the United States in recent years because of the incremental adoption of a pregnancy status checkbox on the standard US death certificate. Using 1999–2017 mortality and birth data, we examined the impact of the pregnancy checkbox on MMRs according to urbanicity of residence (large urban area, medium/small urban area, or rural area), using log-binomial regression models to predict trends that would have been observed if all states had adopted the checkbox as of 1999. Implementation of the checkbox resulted in an average estimated increase of 7.5 maternal deaths per 100,000 live births (95% confidence interval (CI): 6.3, 8.8) in large urban areas (a 76% increase), 11.6 (95% CI: 9.6, 13.6) in medium/small urban areas (a 113% increase), and 16.6 (95% CI: 12.9, 20.3) in rural areas (a 107% increase), compared with MMRs prior to the checkbox. Assuming that all states had the checkbox as of 1999, demographic-factor–adjusted predicted MMRs increased in rural areas, declined in large urban areas, and did not change in medium/small urban areas. However, trends and urban-rural differences were substantially attenuated when analyses were limited to direct/specific causes of maternal death, which are probably subject to less misclassification. Accurate ascertainment of maternal deaths, particularly in rural areas, is important for reducing disparities in maternal mortality.

Introduction

Maternal mortality is a key indicator of population health.[1,2] Monitoring trends in maternal mortality in the United States is important in order to evaluate progress in improving maternal health, make international comparisons, and track inequities by demographic subgroup.[2] Substantial disparities in maternal mortality exist by race/ethnicity and age in the United States,[3,4] and investigators have described rural-urban disparities in recent analyses as well.[5,6]

Maternal mortality is defined by the World Health Organization as the "death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the duration and site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management… but not from accidental or incidental causes",[2] (p. 35). National maternal mortality ratios (MMRs) for the United States were not published for the data years 2004–2017 because of the staggered adoption of the 2003 revision of the US Standard Certificate of Death, which included a pregnancy status checkbox that was added to improve ascertainment of maternal mortality.[7]

In January 2020, MMR estimates based on the new checkbox data were published by the National Center for Health Statistics (NCHS) via the National Vital Statistics System, the official source for US maternal mortality statistics, accompanied by evaluations of the impact of the pregnancy status checkbox.[7,8] While examining the impact of the checkbox during 2003–2017, Rossen et al.[8] found that MMRs estimated during the years after the addition of the checkbox were, on average, higher by 9.6 maternal deaths per 100,000 live births (MMRs increased from approximately 10 maternal deaths per 100,000 live births to 20 per 100,000 live births), with larger increases seen for certain subgroups, such as women aged 35 years or more and non-Hispanic Black women. Notably, after accounting for the staggered implementation of the checkbox and after adjusting for changes in select maternal demographic characteristics over time, they observed no significant change in the overall MMR between 1999 and 2017.[8] Therefore, the observed increases in MMRs that had been reported for the United States in the literature and the popular press may have been largely artifactual, driven by increased counts of maternal deaths related to the staggered implementation of the pregnancy status checkbox by states over time. Other researchers have reported similar findings,[3,9,10] with the checkbox accounting for most (but not necessarily all) of the increase in MMRs. Differences across studies in the degree to which the checkbox explained increases in MMRs may be related to differences in the time periods of analysis, the methods used, and the states included, since most studies were conducted prior to all states' having implemented the checkbox (in 2017).

Although women in rural areas can experience barriers to maternal care, there are few studies of rural-urban disparities in maternal death to date.[5,6,11] As of 2004, more than half of all rural US counties lacked hospital-based obstetrical services, and another 9% experienced the loss of in-county hospital-based obstetrical services during 2004–2014.[12] In addition, rural pregnant women travel farther to access prenatal care and to reach a hospital once labor begins than nonrural women.[13] Rural residents, in general, also experience higher rates of mortality,[14] including infant mortality,[15] as compared with urban residents, and this gap has been widening over time.[16] An analysis of national hospital discharge data suggested that rural areas have higher rates of severe maternal morbidity and mortality than urban areas and that rural areas exhibited larger increases during 2007–2015.[5] However, that study examined a composite outcome measure that included both severe maternal morbidity and in-hospital maternal mortality, essentially reflecting rates of severe maternal morbidity, as it is 50 times more common than maternal death.[17] A recent analysis of data from the Centers for Disease Control and Prevention's Pregnancy Mortality Surveillance System found that pregnancy-related mortality ratios (numbers of pregnancy-related deaths occurring during or within 1 year of pregnancy, per 100,000 live births) from 2011 to 2016 were highest in the most rural areas (mortality ratio = 24.1, 95% confidence interval (CI): 21.4, 27.1) and lowest in large metropolitan areas (mortality ratio = 14.8, 95% CI: 14.2, 15.5).[6] Because neither study examined trends in MMRs over time, trends in rural-urban disparities in maternal mortality in the United States remain unexamined.

The objective of our study's analysis was 3-fold: 1) to estimate the impact of the implementation of the pregnancy status checkbox on MMRs by urbanicity of maternal residence; 2) to estimate trends in MMRs from 1999 through 2017, accounting for the checkbox implementation, by urbanicity of maternal residence; and 3) to examine the impact of potential misclassification of pregnancy status on the death certificate on rural-urban trends in MMRs from 1999 through 2017.

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