Table 2

Description of cohort and data sources used to identify a cohort of births in four high-income countries

LocationCalifornia, USAFinlandNorwayNew South Wales, AustraliaWestern Australia, Australia
Time period1991–20101987–20171980–20161994–20161980–2015
Data sourceOffice of Statewide Health Planning and Development (OSHPD)National Institute for Health and Welfare (THL), Medical Birth RegisterNorwegian Institute of Public Health, Medical Birth RegistryNSW Perinatal Data Collection, NSW Ministry of HealthWA Midwives Data Collection, WA Department of Health
Information availableMaternal characteristics and health conditions; smoking and BMI (2007–2010); pregnancy and labour conditions, antenatal hospitalisations, information on delivery and birth outcomes; gestational age based on LMP estimate (obstetric estimate available for years 2007–2010)Maternal characteristics and health conditions; smoking; pregnancy and labour complications; pregnancy history; details of antenatal care; information on delivery and birth outcomes; health of infant at discharge or 7 daysMaternal characteristics and health conditions; pregnancy and labour complications; medication use during pregnancy; birth outcomes; diagnoses of congenital abnormalities; parental occupation and smoking; births following assisted conceptionMaternal characteristics and health conditions; smoking; pregnancy and labour complications; details of labour; birth outcomes; congenital anomalies, infant and child health outcomesMaternal characteristics and health conditions; smoking; pregnancy and labour complications; details of labour; birth outcomes; congenital anomalies, infant and child health outcomes
Scope of notified birthsAll live births and stillbirths with gestational length ≥20 weeksAll live births and stillbirths with gestational length ≥22 weeks or birth weight ≥500 gAll pregnancies ending after week 12 from 2002 onwards (from week 16 from 1980 to 2001)Gestational length ≥20 weeks or birth weight ≥400 gGestational length ≥20 weeks or birth weight ≥400 g
Linkage methodsProbabilistic linkage based on maternal descriptorsDeterministic linkage of mother based on personal IDDeterministic linkage of mother based on personal IDProbabilistic linkage based on maternal descriptorsProbabilistic linkage based on maternal descriptors
Total births10.9 million1.8 million2.1 million2.2 million1.2 million
Benchmark neonatal morbidity indicators10.5% PTB (LMP estimate)
6.4% LBW
5.8% PTB
4.3% LBW
5.7% PTB
3.4% LBW
5.4% PTB
4.4% LBW
5.3% PTB
5.3% LBW
  • BMI, body mass index; LBW, low birth weight; LMP, last menstrual period; PTB, preterm birth.