1. Public Health, Epidemiology and Biostatistics; School of Health and Population Sciences; University of Birmingham; Birmingham UK
2. Department of Women's and Children's Health; Dunedin School of Medicine; University of Otago; Dunedin New Zealand
3. Department of Preventive and Social Medicine; Dunedin School of Medicine; University of Otago; Dunedin New Zealand
4. NMAHP Research Unit; Glasgow Caledonian University; Glasgow UK
5. Birmingham Women's Hospital; Birmingham Women's NHS Foundation Trust; Edgbaston Birmingham UK
6. Department of Obstetrics and Gynaecology; York Hospital; York UK
7. Health Services Research Unit; University of Aberdeen; Aberdeen UK