1. Department of Obstetrics and Gynecology Hospital Universitario de Torrejón Madrid Spain
2. Department of Obstetrics and Gynecology Hospital Universitario La Paz Madrid Spain
3. Bioestatistics and Epidemiology Platform at Fundación para la Investigación e Innovación Biosanitaria del Principado de Asturias Oviedo Spain
4. School of Health Sciences, Universidad Francisco de Vitoria Pozuelo de Alarcón, Madrid Spain
5. Department of Obstetrics and Gynaecology Prince of Wales Hospital, The Chinese University of Hong Kong Shatin Hong Kong