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Anesth Analg 2001;93:134-141
© 2001 International Anesthesia Research Society

OBSTETRIC ANESTHESIA

Maternal Mortality During Hospital Admission for Delivery: A Retrospective Analysis Using a State-Maintained Database

Sumedha Panchal, MD*, Amelia M. Arria, PhD{dagger}, and Snehalata A. Labhsetwar, MD{ddagger}

*Department of Anesthesiology and Critical Care Medicine, The Johns Hopkins University School of Medicine; {dagger}The Johns Hopkins University School of Hygiene and Public Health, Baltimore, Maryland; and {ddagger}Department of Obstetrics and Gynecology, St. Charles Hospital, Oregon, Ohio

Address correspondence to Sumedha Panchal, MD, Weill Medical College of Cornell University, Department of Anesthesiology, 525 East 68th St., M-329, New York, NY 10021. Address e-mail to sumedhapanchal{at}hotmail.com


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
This study reports the overall age- and race-specific delivery mortality ratios from January 1984 to December 1997 and medical and demographic risk factors associated with maternal death during hospital admission for delivery. We performed a retrospective case control study using patient records from a state-maintained anonymous database of all nonfederal Maryland hospitals that performed deliveries from 1984 to 1997. Variables studied included patient demographics and International Classification of Diseases, 9th Revision, Clinical Modification, diagnosis, and procedure codes. Mortality was the outcome variable. Of the 822,591 hospital admissions for delivery during the 14-yr study period, there were 135 deaths. The overall delivery mortality ratio was 16.4. The most common diagnoses associated with mortality during hospital admission for delivery included preeclampsia/eclampsia (22.2%), postpartum hemorrhage/obstetric shock (22.2%), pulmonary complications (14%), blood clot and/or amniotic embolism (8.1%), and anesthesia-related complications (5.2%). The identification of medical and demographic risk factors may have significant implications creating initiatives aimed at decreasing the public health burden associated with maternal mortality.

Implications: This study reports the medical and demographic risk factors associated withmaternal death during hospital admission for delivery by using astate-maintained database. This information could prove useful in the creationof initiatives aimed at decreasing the public health burden associated withmaternal mortality.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
Maternal death is a particularly tragic event because pregnant women are usually young and healthy (1). The death of a woman during pregnancy or in the period after pregnancy presents a wide array of problems for families and the community (1). The reduction of maternal mortality is a major goal for public health officials in the United States (US) and other developed and developing countries (2). In the US, the 1990 Health Objectives for the Nation included decreasing the maternal mortality for all ethnic groups and geographic areas (3). The Centers for Disease Control and Prevention (CDC) has estimated the current overall maternal mortality ratio (MMR, defined as the number of deaths per 100,000 live births) to be 7.5 (4,5). The goal of the US Public Health Service 2000 Project was to achieve a 50% reduction in the MMR (6,7). More recently, the Healthy People 2010 objectives continue to advocate a decrease in maternal mortality in the US (8).

The measurement and study of risk factors associated with maternal mortality poses several methodological challenges (1). In the US, there are five main sources for identifying maternal deaths, which include published vital records, manual review of death certificates, vital records linkage, review of autopsy reports, and review of medical records (1,9). Reporting from national vital statistics often does not give specific information on all causes of maternal death, attributing more than 40% of all maternal deaths to "other" causes (10,11). Many studies have retrospectively reviewed maternal death certificates to assess maternal mortality rates (4,6,10,12–14). Often, however, death certificates do not provide enough detail to accurately classify the pathophysiology leading to maternal death or to determine contributing risk factors (10,12). In addition, because of these inherent limitations in death certificate data, the degree of underreporting of maternal death rates by routine vital statistics has been estimated to be 20% to 75% (6,9,15).

Maternal death has been defined by the Bureau of Vital Statistics as the death of a woman while pregnant or within 42 days of termination of pregnancy, despite duration and the site of pregnancy, from any cause related to or aggravated by the pregnancy or its management, but not from accidental or incidental causes (6) and by the American College of Obstetricians and Gynecologists (ACOG) as the death of any woman that was caused or contributed to by pregnancy, occurring during pregnancy or within one year after the end of pregnancy (4). The ACOG/CDC and Prevention Maternal Mortality Study Group, a special interest group of ACOG, established voluntary surveillance of maternal deaths in 1983 to improve the detection, collection, and analysis of information pertaining to maternal deaths (4). These variations in definitions of maternal death may contribute to the limitations noted in identification of these deaths by using the previously available sources (9).

There are no published reports of obstetric outcomes examining maternal mortality during hospital admission for delivery by using a state-maintained database. The present study examined maternal mortality during hospital admission for delivery for 14 years in the state of Maryland. The specific aims of this study were to determine overall and age- and race-specific delivery mortality ratios (DMR) from 1984 to 1997 and to identify medical and demographic risk factors associated with maternal mortality during hospital admission for delivery.


   Methods
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 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
The source of the data used for these analyses parallel those used in our previous work examining predictors of intensive care unit admission among obstetric patients (16). Under Maryland law, information on care delivered during all hospital admissions at the 52 nonfederal, short-stay hospitals in Maryland must be reported to the state Health Services Cost Review Committee, which maintains an anonymous database called the Uniform Health Discharge Data Set (UHDDS). In Maryland, most deliveries occur in hospitals and, thus, are subject to the mandatory reporting requirements. Thirty-seven of those 52 hospitals in Maryland deliver obstetric services for childbirth in their facility. Home and birthing center births are not captured in the UHDDS (16).

The UHDDS data were collected beginning in January 1984. Data for the current study were extracted from the UHDDS for a 14-yr period from January 1984 to December 1997. The sampling frame included all patients with Diagnosis Related Grouping (DRG) codes 370–371 for cesarean delivery and DRG codes 372–375 for vaginal delivery discharged from a Maryland hospital. All patients who died during hospital admission for delivery (disposition of death) were selected from the Health Services Cost Review Committee database and defined as "cases" or "maternal deaths." In addition, two "controls," defined as a woman who delivered in the same year, but who did not die during hospital admission for delivery, were randomly selected for each "case." Controls were randomly chosen for each of the 14 yr by using Microsoft Access (Redmond, WA). A random number generator was used to determine a number (n) between 1 and 10. Every nth patient was selected from the universe of patients with a DRG code of 370–375 and disposition of discharge.

Personal characteristics selected included age (<17 yr, 17–34 yr, and >34 yr for advanced maternal age), race (classified in the UHDDS as African-American, Caucasian, Asian or Pacific Islander, American Indian, or other), payment source (government, commercial, or self pay), and marital status (single, married, or other). Hospital variables selected included source of admission (home or transfer from another hospital) and hospital type (major teaching, minor teaching, or community). Hospital status was classified as major teaching if the hospital included both obstetrics/gynecology and anesthesiology accredited graduate medical training programs, minor teaching if the hospital included one of the above training programs; and community if the hospital did not have any of the above training programs. Three of the 37 hospitals that perform obstetric deliveries met the criteria for major teaching hospital; 5 of the 37 hospitals met the criteria for minor teaching hospital; and 29 of the 37 hospitals met the criteria for community hospital. This classification was created to assess whether patients with greater comorbidities were cared for in major/minor teaching hospitals and to allow comparison of maternal mortality in patients among the three defined hospital types (16).

The International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes (17) for the principal discharge diagnosis, the principal procedure, up to 14 secondary discharge and procedure diagnoses from 1994 to 1997, and up to 5 secondary discharge and procedure diagnoses from 1984 to 1993 were reviewed. The Romano-Charlson comorbidity index was used with modification of diagnoses codes to reflect the obstetric population (16,18,19). This index has been used in several other studies (20–22). Anesthesia-related complications during labor and delivery were classified as pulmonary, cardiac, central nervous system, or other complications of anesthesia or sedation in labor and delivery (ICD-9-CM codes 668.0–668.2, 668.8, and 668.9); cardiac complications were defined as postpartum cardiomyopathy (ICD-9-CM code 674.8); cardiac disease was defined as valvular/endocardial disorders (ICD-9-CM code 424); shock during or after labor and delivery was defined as obstetric shock (ICD-9-CM code 669.1); pulmonary complications were defined as aspiration pneumonia, pulmonary edema, acute respiratory failure, and acute respiratory distress syndrome (ICD-9-CM codes 507.0, 518.4, 518.5, and 518.8); cerebrovascular event was defined as cerebrovascular disorder in the puerperium, subarachnoid or intracerebral hemorrhage, and seizure or cerebrovascular accident (ICD-9-CM codes 674.0, 430, 431, 432, and 436); and "other complications of obstetrical surgery and procedures" were defined as cardiac arrest/cerebral anoxia (ICD-9-CM code 669.4).

The main outcome variable studied was mortality. A case-control framework was used to estimate the strength of the association between suspected risk factors and outcomes. The patients who died (cases) during hospital admission for delivery were compared with patients matched in each calendar year who were discharged to home after delivery (controls). These groups were compared on personal characteristics, hospital characteristics, preexisting medical diagnoses, and pregnancy-related medical diagnoses. Significant differences on demographics and hospital characteristics were assessed using univariable logistic regression modeling. Unadjusted odds ratios (OR) with a 95% confidence interval (CI) were used as an index of the strength of the association between each risk factor and mortality. A final multivariable logistic regression model was constructed to evaluate the association between each risk factor and mortality, holding constant all other variables in the model. Because of the very small prevalence of medical diagnoses among the control group, significant differences were assessed with the Fisher’s exact test from two-by-two tables.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
Maternal Mortality
From January 1984 to December 1997, there were 822,591 hospital admissions for delivery in Maryland in the institutions included in the UHDDS. There were 135 deaths during these hospital admissions for delivery. Figure 1 illustrates the delivery mortality ratios for the 14-yr study period. The overall DMR was 16.4, with a range from 5.92 in 1992 to 29.6 in 1985. Although variation was noted in the yearly DMR, no significant temporal trend was observed. The overall age-specific DMR was 13.9 for women aged 34 yr and younger, and 23.9 for women aged older than 34 yr. Figure 2 illustrates the race-specific DMR for the 14-yr study period. Overall, we observed a DMR of 7.6 for Caucasians, 31.6 for African-Americans, and 18.1 for races other than Caucasian or African-American.



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  		Figure 1. Overall delivery mortality ratios in Maryland from 1984 to 1997.

 


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  		Figure 2. Delivery mortality ratios by race in Maryland from 1984 to 1997. 1The delivery mortality ratio for the category defined as other is not included here because of its small sample size. See Table 1 for more information about this group.

 
Risk Factors for Maternal Mortality
The results of the adjusted multiple logistic regression model for prediction of maternal mortality are presented in Table 1. As can be seen, patients who died were significantly more likely to be African-American (60.7% versus 33.3%; OR = 5.4, CI = 2.83–10.1, P < 0.001), to be from another racial category other than Caucasian or African-American (6.7% versus 1.1%; OR = 12.2, CI = 2.63–56.20, P < 0.014), to have undergone a cesarean delivery (60.0% versus 26.7%; OR = 5.3, CI = 3.10–8.98, P < 0.001), to be cared for in a minor teaching hospital (28.1% versus 9.6%; OR = 3.1, CI = 1.60–6.06, P < 0.001), or to be transferred from another hospital (8.9% versus 1.9%; OR = 6.2, CI = 1.66–22.8, P = 0.007). Notably, the adjusted ORs did not vary substantially from the unadjusted ORs obtained from the univariable models, suggesting that race, mode of delivery, hospital type, and source of admission independently and in combination were associated with maternal mortality.


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  		Table 1. Comparison Between Maternal Deaths and Controls on Personal and Hospital Characteristics
 
Table 2 illustrates the pregnancy-related diagnoses associated with maternal mortality ordered by frequency of occurrence during hospital admission for delivery. Compared with controls, cases did not have a significantly larger proportion of preexisting medical diagnoses, which included drug dependence, acquired immunodeficiency syndrome (AIDS), asthma, cardiac disease, diabetes, and hypertension (P > 0.05); however, several differences were observed for pregnancy-related diagnoses. The five most common diagnoses associated with maternal mortality were preeclampsia and/or eclampsia (22.2%), postpartum hemorrhage/obstetric shock (22.2%), pulmonary complications (14.0%), cerebrovascular event (9.6%), and amniotic and/or blood clot embolism (8.1%). Of note, 5 of the 135 maternal deaths (3.7%) and none of the controls had an ICD-9-CM diagnosis (V237) of "insufficient prenatal care." Two of the 135 maternal deaths (1.5%) were associated with trauma.


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  		Table 2. Comparison Between Maternal Deaths and Controls on Medical Diagnoses
 
To gain a fuller understanding of the possible reasons underlying the racial disparity in DMR, a post hoc exploratory analysis of the diagnoses associated with death between African-American and Caucasian women was conducted. Although drug dependence and AIDS were the most common preexisting medical diagnoses associated with mortality in African-American women, only 6.1% and 2.4% of this subgroup had these diagnoses, respectively. The most common pregnancy-related diagnoses associated with mortality in African-American women included postpartum hemorrhage/obstetric shock (26.4%), preeclampsia/eclampsia (25.3%), pulmonary complications (17.6%), anesthesia-related complications (6.6%), and acute renal failure (5.5%) (data not shown in table). In contrast, there were no preexisting medical diagnoses of drug dependence or AIDS associated with mortality among Caucasian women. The most common pregnancy-related diagnoses associated with mortality in Caucasian women included preeclampsia/eclampsia (15.9%), postpartum hemorrhage/obstetric shock (13.6%), blood clot embolism (9.1%), cardiac arrest/cerebral anoxia (9.1%), and cerebrovascular event (9.1%). (The cell sizes were too small to allow for meaningful multivariable analyses stratified by race.) Bivariable modeling without adjustment for cofactors revealed that the differences observed for AIDS, drug dependence, pulmonary complications, and acute renal failure were statistically significant between African-American and Caucasian women.


   Discussion
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 Introduction
 Methods
 Results
 Discussion
References
 
The underreporting of maternal mortality has prompted investigators to review all maternal deaths occurring during pregnancy or a defined postpartum period (1–14). Some authors state that, even with improved maternal reporting of maternal deaths using mortality surveillance programs, these programs do not identify all pregnancy-related deaths (13). The estimated number of maternal deaths in the US is 1.3–3.0 times larger than that reported in vital statistics records (13). Maresh (23) reviewed the process of maternal mortality auditing, the Confidential Enquiries into Maternal Deaths, in the United Kingdom. The auditing of maternal deaths and subsequent production of practice management guidelines have an impact on maternal mortality rates (23). Others have also shown similar benefits of auditing of maternal deaths allowing for comparison of temporal trends in practice (24).

Investigators have examined temporal trends in mortality rates and ratios to gain insight into factors associated with maternal death. The maternal mortality rate is defined as the number of maternal deaths divided by the number of live births during the same reporting period. It provides a ratio, not a true rate, because the denominator does not include the entire population at risk for the outcome described by the numerator (25). Reports have revealed maternal mortality has not declined since 1982 with reports of MMRs ranging from 9.1 to 12.8 (5,6,10). Our study demonstrated an overall DMR of 16.4 with a range from 5.92 to 29.6. The small sample size of maternal deaths in our study precluded conclusions pertaining to temporal changes. It is interesting to note that our findings reflect a DMR more than twice the MMR reported by the CDC (4). The MMRs previously reported in the literature are based on analyses of maternal death certificates (6,9,10,15), unlike the UHDDS. Thus, the degree of underreporting of maternal deaths reported with the use of maternal death certificates may have contributed to the smaller MMRs quoted in the literature (6,9,10,15).

The DMR in our study was found to be larger for women aged more than 34 years. Others have shown women aged 35 years and older to have a 2.6 times increased risk for death than those women aged less than 35 years (12,26). The risks for both chronic disease and complications of pregnancy increase with age (26). Also, women aged 35 years and older are at greater risk than younger women for many adverse reproductive health outcomes (27,28).

Our study estimated that African-American women were 5 times more likely to die during hospital admission for delivery compared with women in other racial categories, and that they comprised 60.7% of maternal deaths. The MMR among women of African-American and other minority races continues to be disturbingly much larger than that among Caucasian women (11,29). Most recently, the CDC found that from 1987 to 1996, African-American women were 4 times more likely than Caucasian women to die during pregnancy or shortly thereafter (30). Some researchers have suggested that race may serve as a marker for other sociodemographic risk factors and cultural differences (31,32). It is still unclear as to the reasons for the continued racial disparities in maternal death; however, several possibilities exist. Social, cultural, economic, and health care access and quality factors may influence maternal mortality (30). Further investigation is warranted to determine the role of different factors leading to the increased MMR observed in African-American women.

Little or no prenatal care during pregnancy greatly increases the risk of experiencing a pregnancy-related death (13,26). Interestingly, our findings revealed an increased prevalence of multiple diagnoses associated with deaths among African-American women, possibly indicating an increased severity of illness among this patient population. In addition, hospital admission for pregnancy complications is far more common than is widely appreciated, and is more frequent among African-American than Caucasian women (33). Creation of initiatives aimed at improving access to prenatal care to women in disadvantaged areas may help reduce these disparities. Sociodemographic, behavioral, and health care system delivery factors may warrant consideration for their potential contribution to the racial disparity between African-American and Caucasian women (30).

An anesthesia-related complication was one of the pregnancy-related diagnoses associated with maternal mortality among African-American women. Death caused by anesthesia-related complications, specifically problems associated with the airway, is the sixth leading cause of pregnancy-related mortality (13,34). Nagaya et al. (35) concluded from a two-year review of maternal death certificates and chart review in Japan that inadequate anesthesia services were associated with maternal mortality. Continued efforts to review and analyze anesthesia-related maternal deaths are warranted to formulate preventative mea-sures for future care.

Approximately 60.0% (versus 33.3%) of the maternal deaths were associated with cesarean delivery. The UHDDS precluded chart review to fully ascertain the circumstances surrounding maternal death in those patients who underwent cesarean delivery (i.e., the UHDDS precluded determination of death secondary to cesarean delivery versus death secondary to complications that required a cesarean delivery). Women undergoing cesarean delivery are certainly a higher-risk group. More importantly, extremely sick parturients may often be delivered emergently, possibly increasing morbidity and mortality associated with emergency cesarean delivery. Our findings are consistent with the work of others who have found that there is an increased association of maternal death for women undergoing cesarean delivery compared with those who have a vaginal delivery (36,37). It is important to note, though, that although cesarean delivery rates in the US increased from 19% to 24% from 1979 to 1990, MMRs have not increased proportionally (12,38).

Teaching hospitals treat a case mix of patients with more severe illness compared with community hospitals (39). They may also see a larger proportion of patients with more comorbidities. Although our findings demonstrated that minor teaching hospital status was associated with maternal mortality, additional research is needed to determine the role, if any, of hospital teaching status on maternal mortality. The transfer of a patient from another hospital was also associated with maternal mortality. The UHDDS, however, precluded determination of the actual hospital source of admission for the hospital transfer. Further investigation is warranted to determine the implications of regionalized obstetric services and maternal transfers on maternal mortality (16).

It is interesting that the three most common diagnoses associated with maternal mortality during hospital admission for delivery (i.e., preeclampsia/eclampsia, postpartum hemorrhage/obstetric shock, and pulmonary complications) are at variance with published reports by Berg et al. (13). They reported that the three most common diagnoses associated with maternal mortality were hemorrhage, embolism, and preeclampsia (13). This may in part be the result of the inclusion in our study of only those maternal deaths occurring during hospital admission for delivery, and hence, a different definition of the time frame for defining maternal death as compared with that reported by Berg et al. (13).

We note several limitations to our study. First, before 1993, the data in the records of the UHDDS included only up to five discharge diagnosis codes and procedure codes for each patient. Thus, we may be limited in describing the comorbidities associated with death for the earlier time period. Second, postpartum patients readmitted to the hospital with complications after discharge from childbirth admission may be missed from analysis (based on DRG coding 370–375). Third, deaths caused by early pregnancy complications (ectopic pregnancy, molar pregnancy, induced and spontaneous abortion) and postpartum complications (readmissions) were not included in the analysis (based on DRG coding 370–375). Fourth, mortality data included only deaths occurring during that hospital admission, and would underestimate pregnancy-related mortality conventionally defined as death occurring up to one year after delivery (1,13). Thus, we selected the term "delivery mortality ratio" to define those deaths occurring only during hospital admission for delivery. Fifth, the UHDDS did not capture home or birthing center births and, thus, may underestimate mortality during admission for delivery. Sixth, the UHDDS did not include the type of anesthesia (regional versus general versus IV sedation) for labor and delivery, making it difficult to determine the incidence of anesthesia-related complications based on anesthesia technique (16). And seventh, the UHDDS precluded assessment of the urgency of the cesarean delivery as all admissions were coded as "admission for delivery" (e.g., without "elective" or "emergent" coding) (16).

Our analysis of a state-maintained database, even with these limitations, allows for examination of trends in maternal mortality associated with labor and delivery, and identification of medical and demographic risk factors associated with maternal morbidity/mortality during hospital admission for delivery. Our analysis may also have value in suggesting a process by which collecting maternal mortality data can be improved. This may yield useful information for the development of preventative intervention strategies. Franks et al. (33) demonstrated the considerable burden of pregnancy morbidity on hospital services. All risk factors, including those related to patient and health care delivery system factors, must be considered when developing strategies aimed at reducing maternal mortality (1).


   Acknowledgments
 
We wish to thank Dr. Srinivasa Raja for his invaluable assistance in preparation of the manuscript.


   References
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

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Accepted for publication January 26, 2001.




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Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press