1 Department of Obstetrics and Prenatal Medicine, Asklepios Clinic Hamburg-Barmbek, Asklepios Medical School, University of Semmelweis, Hamburg, Germany.
2 German Task Force for Obstetrics and Prenatal Medicine, AGG - Section Preterm Birth, Hamburg, Germany.
3 Department of Obstetrics and Gynecology, Marienhaus Klinikum Neuwied, Neuwied, Germany.