1. Department of Obstetrics and Gynecology, Hospital Universitario Puerta de Hierro, 28222 Majadahonda, Spain
2. Department of Obstetrics and Gynecology, Hospital Universitario Materno-Infantil, Las Palmas de Gran, 35016 Canaria, Spain
3. Division of Maternal and Fetal Medicine, Department of Obstetrics and Gynecology, Hospital Universitario La Paz. IdiPAZ, 28046 Madrid, Spain
4. Department of Gynecology, Institut Clínic de Ginecologia, Obstetrícia, i Neonatologia, Hospital Clinic of Barcelona, University of Barcelona, 08036 Barcelona, Spain
5. Delta Ecografía, Centro de Diagnóstico por la Imagen en Obstetricia, Ginecología y Mama, 28006 Madrid, Spain
6. Department of Obstetrics and Gynecology, Clinica Universidad de Navarra, 31008 Pamplona, Spain
7. Department of Obstetrics and Gynecology, Hospital Universitario Ramón y Cajal, 28034 Madrid, Spain