[1] Univ Hosp Trondheim, St Olavs Hosp, Dept Obstet & Gynecol, Trondheim, Norway
[2] Norwegian Univ Sci & Technol, Fac Med & Hlth Sci, Dept Clin & Mol Med, Trondheim, Norway
[3] Norwegian Univ Sci & Technol, Fac Med, Dept Publ Hlth, Trondheim, Norway
[4] Oslo Univ Hosp, Dept Obstet, Oslo, Norway
[5] Innlandet Hosp Trust, Dept Gynecol & Obstet, Elverum, Norway
[6] Stavanger Univ Hosp, Dept Gynecol & Obstet, Stavanger, Norway
[7] Vestre Viken Hosp Trust, Dept Gynecol & Obstet, Drammen, Norway
[8] Sorlandet Hosp, Dept Obstet & Gynecol, Kristiansand, Norway
[9] More & Romsdal Hosp Trust, Alesund Hosp, Dept Obstet & Gynecol, Alesund, Norway
[10] Haugesund Hosp, Dept Gynecol & Obstet, Haugesund, Norway
[11] Ostfold Hosp Trust, Dept Gynecol & Obstet, Gralum, Norway
[12] Haukeland Hosp, Dept Obstet & Gynecol, Bergen, Norway