Maternal Mortality Surveillance, United States, 1980-1985

Lisa M. Koonin, M.N., M.P.H. Hani K. Atrash, M.D., M.P.H. Roger W. Rochat, M.D. Jack C. Smith, M.S.

To better define the incidence, causes, and risk factors associated with maternal deaths, the Division of Reproductive Health, Center for Chronic Disease Prevention and Health Promotion, CDC, coordinated a study by the Maternal Mortality Collaborative, a Special Interest Group of the American College of Obstetricians and Gynecologists (ACOG). In 1983, this group established voluntary surveillance of maternal deaths for the years 1980-1985. The Maternal Mortality Collaborative reported 601 maternal deaths from 19 reporting areas for 1980-1985, representing a maternal mortality ratio of 14.1 per 100,000 live births. Overall, 39% more maternal deaths were reported by the Maternal Mortality Collaborative than by the National Center for Health Statistics for these reporting areas. Overall, women over 30 years of age had a higher risk of dying than did younger women. For each age group, women of black and other races had a greater risk of dying than white women, with women of black and other races who were 30 years and older having the highest risk. The leading causes of maternal deaths were embolism, hypertension in pregnancy, sequelae from ectopic pregnancy, hemorrhage, cerebrovascular accidents, and anesthesia complications. Of the 111 nonmaternal deaths, 90 (82%) were attributed to unintentional or intentional injuries. As a result of the success of this voluntary reporting system, the Division of Reproductive Health initiated National Pregnancy Mortality Surveillance in January 1988.

INTRODUCTION

In April 1987, a major effort was proposed to prevent maternal deaths worldwide (1). In the United States, the Public Health Service's 1990 health objectives for the nation include lowering maternal mortality for all ethnic groups and geographic areas (2). Although maternal mortality is recognized as a public health concern, the magnitude of the problem is often understated, on the basis of routine vital statistics (3). The most recently published epidemiologic study of nationwide maternal mortality provided data on deaths that occurred from 1974 through 1978 (4).

The Center for Chronic Disease Prevention and Health Promotion (CCDPHP), CDC, coordinated a study conducted by the Maternal Mortality Collaborative, a Special Interest Group of the American College of Obstetricians and Gynecologists. This group consisted of representatives from state maternal mortality committees and health departments. In 1983, this group established voluntary surveillance of maternal deaths for the years 1980-1985 to improvethe detection of maternal deaths, to collect and analyze information, and to disseminate the findings to clinicians. Data were submitted to CDC through the chairperson of the Maternal Mortality Special Interest Group on an abstract form developed for this purpose. A preliminary report on the first 39 maternal deaths from this system was published in 1985 (5). MATERIALS AND METHODS

Between April 1983 and May 1987, reports of maternal deaths for selected years between 1980 and 1985 were contributed voluntarily by collaborators from 19 reporting areas of the United States (16 states; New York City; Puerto Rico; and San Jose, California) (Figure 1). According to The National Center for Health Statistics (NCHS), deaths from these 19 areas represented approximately one-third of the maternal deaths in the United States for 1980-1985 (6-11).

After a review of all information provided for each death by the collaborators, a cause of death was assigned to each case according to the International Classification of Diseases, Clinical Modification, Ninth Revision (ICD-9). The deaths were then classified as maternal (either direct or indirect) or nonmaternal (12). A maternal death was defined as a woman's death that was caused or contributed to by pregnancy and that occurred during pregnancy or within 1 year after the end of pregnancy (4,13). A direct maternal death was defined as a death resulting from complications of pregnancy, labor, or delivery or their management. An indirect maternal death was defined as a death in which pregnancy exacerbated a preexisting health problem. A nonmaternal death was defined as a death that occurred during pregnancy or within 1 year after the termination of pregnancy but was considered unrelated to pregnancy (e.g., due to injury, homicide, or suicide).

The subjects' ages were grouped into 5-year periods for analysis. Race was classified as white or as black and other. Hispanics were classified as whites.

Maternal mortality ratios were calculated by using data on live births from NCHS (14-19). Instead of the standard term, "maternal mortality rate," the term "maternal mortality ratio" was used, which more accurately describes the statistic of maternal deaths per 100,000 live births. Maternal mortality ratio is a more accurate term because the numerator includes the number of deaths, regardless of pregnancy outcome (e.g., live birth, stillbirth, ectopic pregnancy), while the denominator includes only the number of live births. Numerators were matched with appropriate denominators by reporting area and year of occurrence. RESULTS

Of the 714 deaths reported to the Collaborative for the years 1980-1985, 601 were classified as maternal and 111 as nonmaternal. In two instances, information regarding the cause of death was insufficient for classification. The maternal mortality ratio was 14.1 deaths per 100,000 live births. Complete statewide reporting was available for 18 of the 19 areas; in California, data were reported from only one city. For those areas of complete reporting, the Collaborative data, based on multiple sources, reflected 39% more maternal (direct and indirect) deaths for the 6-year period than did the NCHS data, based on death certificates alone (6-11).

Most of the decedents were married, were born in the United States, and had a live birth as the outcome of pregnancy (Table 1). The maternal mortality ratio increased with the age of the mother. Overall, women of black and other races had higher maternal mortality ratios than white women (Figure 2). For each age group, women of black and other races had a greater risk of dying than did white women; women of black and other races who were 30 years of age and older had the highest risk (12.6 times higher than that of white women 15-19 years old) (Table 2).

The leading causes of maternal deaths were embolism, indirect causes, hypertension in pregnancy, sequelae from ectopic pregnancy, hemorrhage, stroke, and anesthesia-related complications (Figure 3). The indirect maternal deaths resulted mostly from nonobstetric infections, cardiovascular disease, drug abuse, anemia, and diabetes. The leading causes of death differed by race (Table 3). Women of black and other races were more likely than white women to die from each cause, especially from complications related to ectopic pregnancy, anesthesia, and abortion.

The largest percentage of the deaths occurred during the first 24 hours after the termination of pregnancy (Figure 4). However, 50 (11%) of the deaths occurred more than 42 days after the pregnancy ended (Table 4). The timing of specific obstetric causes of death was unevenly distributed. Most of the deaths that occurred more than 42 days after the pregnancy ended resulted from indirect causes, cardiomyopathy, or embolism.

Of the 111 nonmaternal deaths, 90 (82%) were attributed to unintentional or intentional injuries. A majority (52%) of the injuries were unintentional, mostly due to automobile collisions. The other injuries were intentional, due to homicide or suicide (Figure 5). DISCUSSION

The results from this study were similar to those of previous studies with regard to the increased risk of maternal death for older women and women of black and other races (4,6-11,20,21). Separate analyses by age and race showed that for all age groups, black women had higher ratios of maternal death than white women. In particular, black women who were 30 years of age and older had a much higher risk of dying (12.6 times) than younger white women.

The Maternal Mortality Collaborative identified embolism, indirect causes, hypertensive disease of pregnancy, ectopic pregnancy complications, and stroke as the leading causes of maternal death. These findings also were similar to those of previous studies (4). Cause-specific mortality rates could not be calculated because appropriate denominators were not available for all causes of death. Instead, cause-specific mortality ratios were used to allow comparison with other published studies.

Maternal mortality ratios also differed by race for each cause of death. Previous studies have shown that women of black and other races have about three times higher mortality ratios related to complications of induced abortion and ectopic pregnancy than do white women (22,23).

Since 11% of maternal deaths occurred between 42 days and 1 year after the pregnancy ended, definitions of maternal death that limit the period between termination of pregnancy and death to 42 days may result in the incorrect classification of deaths that are caused by pregnancy or pregnancy complications.

Counts of maternal deaths and maternal mortality rates based on vital statistics are published annually by NCHS. The most recently published statistics are for 1986 (24). The NCHS counts are based entirely on the physician's certification of the cause of death on the death certificate, which NCHS processes and tabulates according to the classification system, definitions, and rules for selecting underlying cause of death specified by the World Health Organization (WHO) in the ICD-9. According to WHO, "A maternal death is defined 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."

Death from injury accounted for most of the nonmaternal deaths. In the United States, intentional and unintentional injuries are a leading cause of death for reproductive-age women (25,26). In one state, studies of maternal mortality revealed that injury was the leading cause of nonmaternal deaths for 1982-1985 (27). Some nonmaternal injuries probably are missed because these deaths are not routinely identified and analyzed by maternal mortality committees (28).

The results of this study suggest that more complete information on maternal deaths may be obtained from a voluntary reporting system that uses intensive case detection and reporting by multiple sources than from national vital statistics alone. The number of maternal deaths identified in this study was 39% higher than that published by NCHS for the same reporting areas and time period. This discrepancy was due, in part, to the different definitions of maternal mortality; NCHS counted only those deaths that occurred within 42 days after termination of pregnancy, and the Collaborative counted deaths that occurred up to 1 year after termination. However, even after an allowance was made for the difference in definitions, the Maternal Mortality Collaborative still reported 29.5% more maternal deaths than did NCHS.

Even though data from the Collaborative are more representative than those for any single state or region, they cannot be generalized to the total United States population.

Although the definition for maternal death used by the Collaborative was broader than that used for national vital statistics, an understatement of maternal deaths still could have occurred. Misclassification of maternal deaths has been well documented in a number of nationwide and statewide studies (3,29-30). In addition, information submitted for many of the cases was derived only from death certificates, which provided scant information about causes of death, risk factors, and obstetrical history; therefore, only limited conclusions about the risk of maternal death could be drawn.

At present, vital statistics collected by NCHS are the only source of information about U.S. ratios of maternal mortality. Until January 1988, no systematic, national system existed for studying the epidemiology of maternal mortality. Some states collect and publish state ratios of maternal mortality; however, both the national and the state vital statistics systems have several limitations.

First, information reported from vital statistics alone is limited. Death certificates alone may not provide adequate information on the sequence of events that led to death. Ultimately a single code is assigned to classify the underlying cause of death. Often, however, several factors may contribute to a death; therefore, the death cannot be adequately described with a unidimensional code (31). In this study, although we used a single code for classifying each of the deaths, we also assigned multiple causes of death if appropriate. Almost half of the cases (48%) had multiple cause of death codes used to describe the series of events leading to death.

Second, no standard, scientifically valid definitions of maternal death are used by all researchers and clinicians. The differences in the period between termination of pregnancy and death used in defining maternal mortality is one example of a definitional difference that can cause variations in case detection and reporting. NCHS uses 42 days in its definition (32); the American Medical Association, 90 days (33); the American College of Obstetricans and Gynecologists, 42 days (34); and the Maternal Mortality Collaborative, 1 year.

Finally, the coding system used by national vital statistics and states to describe maternal deaths includes a combination of outcomes of pregnancy (e.g. ectopic pregnancy, abortion), immediate causes of death (e.g., hemorrhage), and underlying obstetrical conditions that contribute to death (e.g., obstructed labor). This system of classification precludes a determination of the real causes of maternal death. To develop strategies to prevent maternal deaths, public health personnel need to know the immediate cause of death as well as the underlying conditions that led to death.

Because of the success of this voluntary reporting system, the Division of Reproductive Health, CCDPHP, initiated National Pregnancy Mortality Surveillance in January 1988 (35). This system was designed to overcome some of the limitations inherent in the present systems. In the new system, multiple sources of reporting and of information are used to identify and investigate all reported pregnancy-associated deaths in the United States. Sources included vital records; reports from maternal mortality committees, practicing physicians, and private citizens; medical examiners' reports; scientific literature; and special studies or surveys. This surveillance system also introduces a new method for assigning causes of death to each case upon complete investigation. Death certificates of pregnant women are matched with birth certificates and fetal death certificates to provide a basis for analysis. In addition, autopsy reports, coroners' reports, and medical records are used to determine the cause of death and the factors that placed women at increased risk of maternal death. Through this new system, the outcomes of pregnancy will be analyzed separately from the immediate causes of death. For example, if a woman died from complications of ectopic pregnancy because of a ruptured fallopian tube that led to hemorrhage, the immediate cause of death (hemorrhage) would be analyzed as well as the pregnancy outcome (ectopic pregnancy).

The success of this new system will depend on data reported from various sources, such as state health departments, maternal mortality committees, and individual practitioners. More detailed information about this system may be obtained by calling the Pregnancy Epidemiology Branch at (404) 639-3131 or the Research and Statistics Branch at (404) 639-3392, or by writing to Pregnancy Mortality Surveillance, Division of Reproductive Health, Center for Chronic Disease Prevention and Health Promotion, Mailstop CO6, Centers for Disease Control, Atlanta, Georgia 30333.

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