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Estimating miscarriages

There is no accurate method for counting miscarriages that do not result in hospitalization as an inpatient. Many countries, in fact, do not include miscarriages in their pregnancy calculations, and use only the more reliable numbers: live births, induced abortions and stillbirths. International comparisons, therefore, can be problematic. Two other approaches to estimating miscarriages have been taken: the use of survey data on fertility and a formula based on fetal life tables.

Based on the 1984 Canadian Fertility Survey, the miscarriage ratio (miscarriages to 100 live births) was 16.4 for women of all ages.¹⁷ This figure was in line with an earlier study, which estimated miscarriages to be approximately 15% of all pregnancies.¹⁸ However, that survey is now 16 years old, and the ratio may have changed. A more recent publication using US data estimated that miscarriages end 19% of all pregnancies. The formula for this estimate accounted for miscarriages of pregnancies that might have gone to term and for miscarriages that might have occurred had an abortion not been performed.¹⁹ While this study is limited by its use of weekly fetal life tables from 1980 for New York City, the author argues that it is adequate for generalizations for the United States. The Alan Guttmacher Institute estimates miscarriages as 20% of live births plus 10% of abortions.²⁰ Their calculation of pregnancy rates takes account of live births, stillbirths, induced abortions, and estimated miscarriages.

The US National Center for Health Statistics (NCHS) and the Centers for Disease Control and Prevention also publish teenage pregnancy rates for the United States and use data from the 1982, 1988 and 1995 National Surveys of Family Growth to estimate miscarriages. Their numbers are slightly higher than those of the Guttmacher Institute. For instance, the 1996 NCHS estimate of pregnancy rates for 15- to 19-year-olds in the US was 98.7 per 1,000, compared with 97.3 per 1,000 reported by the Alan Guttmacher Institute.²¹

Teenage pregnancy rate, women aged 15 to 19, by method of measuring miscarriages, Canada, 1997


Data source: Health Statistics Division
† Conventional method used for calculating miscarriages in Canada,
and the one used for all data presented in this article.