1 Department of Obstetrics, Oslo University Hospital, Oslo, Norway; University of Oslo, The Medical Faculty, Oslo, Norway. Electronic address: Annetine.Staff@ous-hf.no.
2 South-Eastern Norway Regional Health Authorities, Norway.
3 Department of Obstetrics, Oslo University Hospital, Oslo, Norway; University of Oslo, The Medical Faculty, Oslo, Norway.
4 Department of Anesthesiology, Oslo University Hospital, Oslo, Norway.
5 Department of Obstetrics and Gynecology, St Olav's Hospital, Trondheim, Norway.
6 Department of Obstetrics, Oslo University Hospital, Oslo, Norway.
7 Department of Obstetrics and Gynecology, Haukeland University Hospital, Bergen, Norway.
8 Department of Obstetrics and Gynecology, Tromsø University Hospital, Tromsø, Norway.