1. Department of Public Health; Health Service Research Unit; Institute of Health Sciences Old Road Oxford UK OX3 7LF
2. University of Leeds; Centre for Epidemiology and Biostatistics; Bradford Royal Infirmary, Bradford Institute of Health Research Temple Bank House, Duckworth Lane Bradford West Yorkshire UK BD9 6RJ
3. Queen Elizabeth II Research Institute; NSW Centre for Perinatal Health Services Research; Building DO2 University of Sydney Sydney NSW Australia 2006
4. Royal Women's Hospital; Department of Perinatal Medicine; Carlton Victoria Australia 3053