1. Department of Obstetrics and Gynaecology, El Escorial University Hospital, 28200 Madrid, Spain
2. Faculty of Medicine, Universidad Francisco de Vitoria, 28223 Madrid, Spain
3. Faculty of Health Sciences, Universidad Francisco de Vitoria, 28223 Madrid, Spain
4. Department of Obstetrics and Gynaecology, Sierra de Guadarrama Health Centre, 28440 Madrid, Spain
5. Department of Obstetrics and Gynaecology, La Paz University Hospital, 28046 Madrid, Spain
6. Department of Obstetrics and Gynaecology, San Carlos Clinic Hospital, 28040 Madrid, Spain