Our international comparisons used data for 2004, which were available from Australia, Canada, countries in Europe, and the United States. We also made comparisons using data for 2007 from Australia, Canada, and New Zealand.
Data for Canada came from the vital registration files of Statistics Canada and the hospital admission files of the Canadian Institute for Health Information. These data included information on all stillbirths, live births, neonatal deaths (0-27 days after birth), and infant deaths (0-364 days after birth) in Canada in 2004 from Statistics Canada files and all hospital live births, stillbirths, and infant deaths during the birth admission in the fiscal year 2007-8 from the discharge abstract database of the Canadian Institute for Health Information.15
For study purposes, we excluded births from the province of Ontario from Statistics Canada data because of concerns about quality,15
and hospital admission data did not include information from the province of Quebec.
Data for Australia (stillbirths in 2004 and neonatal deaths in 2007) and New Zealand (2007) came from published annual reports which provided the birth weight and gestational age of births and deaths.16
Data for countries in Europe for 2004 came from the European Perinatal Health Report and other publications.18
The European Perinatal Health Report contained data on live births, stillbirths, neonatal deaths, and infant deaths for all European countries; in this study, we included only countries with complete birthweight specific (or gestational age specific) information on births and deaths.
Information on live births, stillbirths, neonatal deaths, and infant deaths in the United States came from the period infant mortality files of the National Center for Health Statistics for 2004. Information in these files was collated from birth and death certificates. For gestational age specific comparisons of neonatal mortality rates, we used the clinical estimate of gestation, as this is more reliable and corresponds more closely with estimates of gestational age from other countries.21
Stillbirths were identified in accordance with the definition of the Centers for Disease Control and Prevention (as fetal deaths with a gestational age at birth of 20 weeks or greater).24
We calculated the reported proportion of live births and the reported proportion of neonatal deaths at the lower end of the range of birth weight and gestational age in each country (that is, those with a birth weight under 500 g or under 1000 g or a gestational age of less than 24 weeks or less than 28 weeks). We assessed the validity of using neonatal mortality rates for ranking countries’ performance by examining ranks based on crude neonatal mortality rates and ranks based on neonatal mortality rates calculated after exclusion of live births with a known birth weight under 1000 g (or a known gestational age of less than 28 weeks). Our primary analysis focused on mortality rates calculated after exclusion of live births under 1000 g (rather than rates calculated after exclusion of live births at less than 28 weeks) because of international variations in the modalities used to measure gestational age (menstrual based dating, early ultrasound dating, first trimester ultrasound dating, paediatric examination, and so on).
We also assessed international variation in crude infant mortality and stillbirth rates and contrasted this with variation in infant mortality and stillbirth rates calculated after exclusion of births under 1000 g birth weight (or less than 28 weeks’ gestation). Mortality calculations that excluded births under 1000 g birth weight (or less than 28 weeks’ gestation) retained births with missing birth weight (or gestational age). Finally, we calculated mortality rate ratios, 95% confidence intervals, and P values to assess the magnitude and statistical significance of observed differences. For these comparisons, we used the United States as the reference category for neonatal mortality, Canada for infant mortality, and Australia for fetal mortality. We used EpiInfo and SAS version 9.2 for analyses.