OBJECTIVE: Concerns about differences in registration practices across countries have limited the use of routine data for international very preterm birth (VPT) rate comparisons. DESIGN: Population-based study. SETTING: Twenty-seven European countries, the United States, Canada and Japan in 2010. POPULATION: A total of 9 376 252 singleton births. METHOD: We requested aggregated gestational age data on live births, stillbirths and terminations of pregnancy (TOP) before 32 weeks of gestation, and information on registration practices for these births. We compared VPT rates and assessed the impact of births at 22-23 weeks of gestation, and different criteria for inclusion of stillbirths and TOP on country rates and rankings. MAIN OUTCOME MEASURES: Singleton very preterm birth rate, defined as singleton stillbirths and live births before 32 completed weeks of gestation per 1000 total births, excluding TOP if identifiable in the data source. RESULTS: Rates varied from 5.7 to 15.7 per 1000 total births and 4.0 to 11.9 per 1000 live births. Country registration practices were related to percentage of births at 22-23 weeks of gestation (between 1% and 23% of very preterm births) and stillbirths (between 6% and 40% of very preterm births). After excluding births at 22-23 weeks, rate variations remained high and with a few exceptions, country rankings were unchanged. CONCLUSIONS: International comparisons of very preterm birth rates using routine data should exclude births at 22-23 weeks of gestation and terminations of pregnancy. The persistent large rate variations after these exclusions warrant continued surveillance of VPT rates at 24 weeks and over in high-income countries. TWEETABLE ABSTRACT: International comparisons of VPT rates should exclude births at 22-23 weeks of gestation and terminations of pregnancy.

Centre for Disease Prevention and Control of Latvia Riga Latvia

Department Child Health TNO The Netherlands Organisation for Applied Scientific Research Leiden The Netherlands Department Public Health Faculty of Medical Sciences Anton de Kom University of Suriname Paramaribo Suriname

Department of Epidemiology and Biostatistics National Research Institute of Mother and Child Warsaw Poland

Department of Epidemiology Rollins School of Public Health Emory University Atlanta GA USA

Department of Lifecourse Epidemiology Department of Social Medicine National Centre for Child Health and Development Setagayaku Tokyo Japan

Department of Obstetrics and Gynecology and Women's Health Albert Einstein College of Medicine Montefiore Medical Center Bronx NY USA

Departments of Pediatrics and of Epidemiology Biostatistics and Occupational Health McGill University Faculty of Medicine Montreal QC Canada

Estonian Institute for Population Studies Tallinn University Tallinn Estonia

Inserm UMR 1153 Obstetrical Perinatal and Pediatric Epidemiology Research Team Centre for Epidemiology and Statistics Sorbonne Paris Cité DHU Risks in Pregnancy Paris Descartes University Paris France

Institute for the Care of Mother and Child Prague Czech Republic

Surveillance and Epidemiology Division Centre for Chronic Disease Prevention Public Health Agency of Canada Ottawa ON Canada

The Infant Mortality and Morbidity Studies Group Department of Health Sciences College of Medicine Biological Sciences and Psychology University of Leicester Leicester UK

THL National Institute for Health and Welfare Helsinki Finland Karolinska Institute Department of Neurobiology Care Sciences and Society Division of Family Medicine Stockholm Sweden

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