Health Economics Unit, Institute of Applied Health Research, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, UK. Tommy's National Centre for Miscarriage Research, Institute of Metabolism and Systems Research, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, UK. Biostatistics, Evidence Synthesis and Test Evaluation, Institute of Applied Health Research, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, UK. Department of Obstetrics and Gynaecology, Frere Hospital, University of the Witwatersrand, University of Fort Hare, Eastern Cape Department of Health, East London, Eastern Cape, South Africa. Health Economics Unit, Institute of Applied Health Research, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, UK. t.e.roberts@bham.ac.uk.