IJE Advance Access originally published online on September 20, 2008
International Journal of Epidemiology 2009 38(2):480-489; doi:10.1093/ije/dyn194
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A comparison of foetal and infant mortality in the United States and Canada
1 Division of Epidemiology and Biostatistics, Department of Obstetrics, Gynecology, and Reproductive Sciences, UMDNJ-Robert Wood Johnson Medical School, New Jersey, USA.
2 Maternal and Infant Health Section, Health Surveillance and Epidemiology Division, Public Health Agency of Canada, Ottawa, Canada.
3 Perinatal Epidemiology Research Unit, Departments of Obstetrics and Gynaecology, and Pediatrics, Dalhousie University and the IWK Health Centre, Halifax, Canada.
4 Departments of Pediatrics and of Epidemiology and Biostatistics, McGill University, Montreal, Canada.
* Corresponding author: Division of Epidemiology and Biostatistics, Department of Obstetrics, Gynecology, and Reproductive Sciences, UMDNJ-Robert Wood Johnson Medical School, 125 Paterson Street, New Brunswick, NJ 08901-1977, USA. E-mail: cande.ananth{at}umdnj.edu
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Abstract |
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Background Infant mortality rates are higher in the United States than in Canada. We explored this difference by comparing gestational age distributions and gestational age-specific mortality rates in the two countries.
Methods Stillbirth and infant mortality rates were compared for singleton births at 
22 weeks and newborns weighing 500 g in the United States and Canada (1996–2000). Since menstrual-based gestational age appears to misclassify gestational duration and overestimate both preterm and postterm birth rates, and because a clinical estimate of gestation is the only available measure of gestational age in Canada, all comparisons were based on the clinical estimate. Data for California were excluded because they lacked a clinical estimate. Gestational age-specific comparisons were based on the foetuses-at-risk approach.
Results The overall stillbirth rate in the United States (37.9 per 10 000 births) was similar to that in Canada (38.2 per 10 000 births), while the overall infant mortality rate was 23% (95% CI 19–26%) higher (50.8 vs 41.4 per 10 000 births, respectively). The gestational age distribution was left-shifted in the United States relative to Canada; consequently, preterm birth rates were 8.0 and 6.0%, respectively. Stillbirth and early neonatal mortality rates in the United States were lower at term gestation only. However, gestational age-specific late neonatal, post-neonatal and infant mortality rates were higher in the United States at virtually every gestation. The overall stillbirth rates (per 10 000 foetuses at risk) among Blacks and Whites in the United States, and in Canada were 59.6, 35.0 and 38.3, respectively, whereas the corresponding infant mortality rates were 85.6, 49.7 and 42.2, respectively.
Conclusions Differences in gestational age distributions and in gestational age-specific stillbirth and infant mortality in the United States and Canada underscore substantial differences in healthcare services, population health status and health policy between the two neighbouring countries.
Keywords Stillbirth, infant mortality, preterm delivery, clinical estimate of gestation, foetuses-at-risk, neonatal intensive care, Kitagawa analysis
Accepted 19 August 2008