1. Division of Prenatal Medicine, Department of Obstetrics and Gynecology , University Hospital Muenster , Albert-Schweitzer-Str. 1 , 48149 Muenster , Germany , Tel.: +49172 5787653, Fax: +49 (0)251/83 – 48167
2. Institute of Biostatistics and Clinical Research , University of Muenster , Muenster , Germany
3. Department of Obstetrics and Gynecology , University Hospital Muenster , Muenster , Germany