1. Thomas Jefferson University; Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology; 833 Chestnut Street Level 1 Philadelphia Pennsylvania USA PA 19107
2. BMJ; BMJ-TAG; BMA House, Tavistock Square London UK WC1H 9JR
3. School of Medicine, University of Naples Federico II; Department of Neuroscience, Reproductive Science and Dentistry; 5 Pansini Naples Italy 80100
4. Brighton and Sussex University Hospitals NHS Trust; Department of Obstetrics and Gynaecology; Royal Sussex County Hospital Eastern Road Brighton UK BN2 5BE