作者单位:Biostatistics Unit, Valme University Hospital, Sevilla, Spain[1]Department of Obstetrics and Gynaecology, Hospital University Valme, Avd. Cadiz S/N., Sevilla, Spain[2]Department of Obstetrics and Gynaecology, Hospital University Valme, Avd. Cadiz S/N., Sevilla[3]