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Misclassification of Maternal Deaths -- Washington State

To determine more accurately the number of maternal deaths in the State of Washington in the period 1977-1984, death certificates for all reproductive-age women who died in those years were linked to birth and fetal-death files. The purpose of this linkage was to identify women who had died within a year after having a live birth or fetal death. For this 8-year period, the record linkage identified 23 maternal deaths (Table 3) in addition to the 34 maternal deaths reported through the state's vital statistics system. This total of 57 represents a 68% increase in ascertainment of maternal deaths.

To establish linkage, the names of the 2,073 women, ages 15-44 years, who had died in Washington State in 1977-1984 from causes other than cancer and intentional or unintentional injuries, were compared with the names of women on birth and fetal-death files. When these names matched, birth and death certificates were compared to verify each match. The woman's cause of death, the interval between delivery and death, and other medical information about the case were reviewed to determine whether the death should be classified as maternal (Table 3). Maternal mortality was defined as either a direct or indirect maternal death occurring within 42 days of delivery, based on the codes defined by the International Classification of Diseases (1,2).

Of the 34 maternal deaths reported through the state's vital statistics system, 20 were linked to birth or fetal-death certificates; 14 women had a maternal condition listed as the cause of death, but were not linked to birth or fetal-death certificates. In addition, death certificates for 39 other women were matched with birth or fetal-death certificates, but these deaths had not been classified by the state's vital statistics system as maternal deaths. For 16 of these 39 deaths, a causal association with pregnancy was unclear or unlikely; the other 23 were classified as maternal. Seven of the 23 maternal deaths that were originally misclassified as non-maternal were concurrent with the reported birth or fetal death. Reported by P Starzyk, PhD, F Frost, PhD, JM Kobayashi, MD, State Epidemiologist, Washington Dept of Social and Health Svcs; Pregnancy Epidemiology Br, Research and Statistics Br, Div of Reproductive Health, Center for Health Promotion and Education, CDC.

Editorial Note

Editorial Note: There was a decrease in misclassified deaths in Washington State between 1977 and 1984. In the period 1977-1981, 19 (53%) of 36 maternal deaths were originally misclassified as non-maternal (3). In contrast, in 1982-1984, only four (19%) of 21 maternal deaths were originally misclassified. The decrease in misclassified maternal deaths in 1982-1984 probably reflects an increased number of queries by the nosologists during this period. A review of maternal death certificates in Washington showed that 60% of the maternal deaths were queried from 1982 through 1984, in contrast to 15% from 1977 through 1981.

Based on the state's vital statistics, the maternal mortality rate in Washington was 6.5 maternal deaths/100,000 live births for this 8-year period. However, the rate calculated from both vital statistics and record linkage was 10.9/100,000 live births. Underestimation of maternal mortality is a problem that has long been recognized (4,5). The Washington State study--as well as recent studies in Georgia, New Jersey, and Puerto Rico--suggests that the problem persists (6,7,8). The percentage of maternal deaths not obtainable from routine coding of death certificates ranged from 27% in Georgia to 71% in Puerto Rico. As was shown in Georgia (6), this study demonstrates that more complete counts of maternal deaths can be obtained from routine linkage of birth and fetal-death certificates with death certificates of reproductive-age women.

Several categories of maternal deaths may not be found through record linkage if they are misclassified on death certificates. The first category includes maternal deaths that may not generate a record of pregnancy outcome. This includes maternal deaths from ectopic pregnancy, gestational trophoblastic disease, induced abortion, and first-trimester spontaneous abortion, as well as maternal deaths that occur during pregnancy. The second category includes maternal deaths that are misclassified but are not identified by record linkage because of incorrect identifiers (e.g., name, address, and birth date) or because of unreported births or fetal deaths. Some of these maternal deaths can be identified by supplementing information from vital statistics with annual maternity service reports from hospitals and with individual reports from physicians, hospitals, and medical examiners (7). Furthermore, as was shown in Puerto Rico (8), a review of death certificates and selected medical records of reproductive-age women who died could probably identify even more of these maternal deaths.

In 1983, the reported maternal mortality rate in the United States was 8.0/100,000 live births (9). The U.S. Public Health Service 1990 Objective for maternal mortality is a maternal death rate not to exceed 5/100,000 live births for any county or for any ethnic group. Accurate and complete data on maternal deaths may facilitate the development of strategies to reduce the maternal mortality rate. In the near future, the Center for Health Promotion and Education, CDC, plans to establish a National Maternal Mortality Surveillance System to assist in achieving this objective.

References

  1. National Center for Health Statistics. Instructions for classifying the underlying cause of death, 1976-1978. Vital statistics, part 2A. Hyattsville, Maryland: Department of Health and Human Services, Public Health Service, National Center for Health Statistics, 1976.

  2. National Center for Health Statistics. Instructions for classifying the underlying cause of death, 1979. Vital statistics, part 2A. Hyattsville, Maryland: Department of Health and Human Services, Public Health Service, National Center for Health Statistics, 1978.

  3. Benedetti TJ, Starzyk P, Frost F. Maternal deaths in Washington State. Obstet Gynecol 1985;66:99-101.

  4. Barno A, Freeman DW, Bellville TP. Minnesota maternal mortality study; five-year general summary, 1950-1954. Obstet Gynecol 1957;9:336-44.

  5. Jewett JF. Changing maternal mortality in Massachusetts. N Engl J Med 1957;256:395-400.

  6. Rubin G, McCarthy B, Shelton J, Rochat RW, Terry J. The risk of childbearing re-evaluated. Am J Public Health 1981;71:712-6.

  7. Ziskin LZ, Gregory M, Kreitzer M. Improved surveillance of maternal deaths. Int J Gynaecol Obstet 1979;16:281-6.

  8. Speckhard ME, Comas-Urrutia AC, Rigau-Perez JG, Adamsons K. Intensive surveillance of pregnancy-related deaths, Puerto Rico, 1978-1979. Bol Asoc Med PR 1985;77:508-13.

  9. National Center for Health Statistics. Advance report of final mortality statistics, 1983. Monthly Vital Statistics Report 1985;34:38.



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