1. Department of Obstetrics and Gynecology, Hospital Universitario Miguel Servet, Zaragoza, Spain
2. Department of Obstetrics and Gynecology, Hospital General de Villalba, Collado Villalba, Spain
3. Escuela Universitaria Politécnica de la Almunia, Universidad de Zaragoza, La Almunia de Doña Godina, Spain
4. Department of Statistical Methods and Institute for Biocomputation and Physics of Complex Systems-BIFI, Universidad de Zaragoza, Zaragoza, Spain