Background. Our aim was to study the impact of record linkage and different classification principles on maternal mortality rate.
Methods. The death certificates of all fertile-aged women who died in 1987-94 in Finland (n = 9,192) were linked to the Birth, Abortion, and Hospital Discharge Registers (n=513,472 births, 93,807 induced abortions, and 71,701 other ended pregnancies) to identify the women who had been pregnant during their last year of life. All deaths that occurred up to 1 year after the end of pregnancy were classified according to their connection to pregnancy. Results. In total, 281 qualifying deaths were found. Only in 22% of the death certificates was the pregnancy or its end mentioned. The mortality rate was 41 per 100,000 registered ended pregnancies (27 for births, 48 for miscarriages or ectopic pregnancies, and 101 for abortions). The maternal mortality rate depended greatly on which of these 281 cases were defined as maternal deaths. The early maternal mortality rate varied between 5.6 and 6.8 per 100,000 live births, and the late maternal mortality rate between 0.6 and 2.5 depending on the definition used. The classification of other than direct maternal deaths was ambiguous, especially in case of late cancers, cardio- and cerebrovascular diseases, and early suicides. The official Finnish figure for early maternal mortality (6.0/100,000 live births) seems to be a good estimate, although only 65% of individual deaths were unambiguously classified.
Conclusions. Register linkage is necessary to identify late maternal deaths and pregnancy-associated deaths. The current official classification of maternal deaths as indirect, direct and fortuitous is arbitrary and allows much variation in defining a maternal death.