The Maternal Mortality Incidence Rate (MMIR)
Timothy Riffe, Centre d’Estudis Demogràfics (CED)
This paper proposes the estimation of maternal mortality with the use of an occurrence/exposure rate (hazard), the maternal mortality incidence rate (MMIR), which places maternal exposure in the denominator. Estimation of maternal exposure requires information on the numbers and average durations of live births, early and late fetal deaths, induced abortions, ectopic pregnancies and on twinning rates. An example estimate of age-specific MMIR is provided for the case of the United States, 2002. The commonly used maternal mortality ratio (MMR) is concluded to overestimate maternal mortality in the extreme ages of childbearing, but to underestimate it in the peak ages of childbearing. Calculated as a crude ratio, MMR has been subject to underestimation due to denominator distortion, a trend that increased in magnitude over the years 1997-2004. I, however, recommend the continued use of MMR based on its relative ease of calculation and continued uncertainty regarding maternal exposure in MMIR.