1. Policy Research Unit in Maternal Health and Care; National Perinatal Epidemiology Unit; Nuffield Department of Population Health; University of Oxford; Oxford UK
2. Maternal and Fetal Health Research Centre; Faculty of Biology, Medicine and Health; University of Manchester; Manchester UK
3. St Mary's Hospital; Manchester Academic Health Science Centre; Central Manchester University Hospitals NHS Foundation Trust; Manchester UK
4. Health Economics Research Centre; Nuffield Department of Population Health; University of Oxford; Oxford UK