Comparability of published perinatal mortality rates in Western Europe: the quantitative impact of differences in gestational age and birthweight criteria.

OBJECTIVE: To quantify the impact of publication criteria on differences in published national perinatal mortality rates among Western European countries. DESIGN: Descriptive study of perinatal mortality rates in Western European countries with adjustments for international differences in publication data. POPULATION: All live births and perinatal deaths in 1994 in Western European countries. METHODS: The 1994 perinatal mortality rates were obtained from national and Eurostat publications for Belgium, Denmark, Finland, France, Germany, Greece, The Netherlands. Norway, Portugal, Spain, Sweden, United Kingdom (England, Wales, Scotland, Northern Ireland). Two methods, one direct and one indirect, were used for adjusting these officially published rates for differences in registration laws or publication practices. For the indirect method adjustment factors were derived from an analysis of a large Finnish database using different cutoff points for gestational age and birthweight. For the direct method a common cutoff point was imposed for birthweight (1000g) and gestational age (28 completed weeks) on national perinatal mortality data, obtained from civil registration or hospital/obstetrics databases in each country. RESULTS: The published perinatal mortality rates ranged from 5.4 per 1000 total births in Sweden and Finland to 9.7 in Greece and Northern Ireland. The indirect adjustment method showed that some countries apply cutoff points for registration or publication of perinatal mortality which may raise the perinatal mortality rate by up to 17% above the most commonly used threshold for including live and stillbirths. The direct adjustment method showed that a common lower limit of 1000g for birthweight or 28 weeks for gestational age would reduce the perinatal mortality rate, but by a differing extent ranging from 14% to 40%. Both adjustment methods reduced the contrast between the countries' perinatal mortality rates, and changed their rank order. CONCLUSION: These quantitative results confirm that international differences in countries' published perinatal mortality rates partly reflect differences between countries' criteria for registration and publication of perinatal deaths.