1. University of Leeds; Centre for Epidemiology and Biostatistics; Bradford Institute for Health Research Bradford Royal Infirmary, Duckworth Lane Bradford West Yorkshire UK BD9 6RJ
2. Queen Elizabeth II Research Institute; NSW Centre for Perinatal Health Services Research; Building DO2 University of Sydney Sydney NSW Australia 2006
3. The University of Liverpool; C/o Cochrane Pregnancy and Childbirth Group, School of Reproductive and Developmental Medicine, Division of Perinatal and Reproductive Medicine; First Floor, Liverpool Women's NHS Foundation Trust Crown Street Liverpool UK L8 7SS
4. World Health Organization; UNDP/UNFPA/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction, Department of Reproductive Health and Research; 20 Avenue Appia Geneva Switzerland 1211