[1] Karolinska Inst, Danderyd Hosp, Dept Clin Sci, Div Obstet & Gynecol, S-18288 Danderyd, Sweden
[2] Karolinska Inst, Dept Med Epidemiol & Biostat, Stockholm, Sweden
[3] Univ Helsinki, Cent Hosp, Dept Obstet & Gynecol, Jorvi Hosp, Espoo, Finland
[4] Univ Oslo, Akershus Univ Hosp, Dept Obstet & Gynecol, Lorenskog, Norway
[5] Aarhus Univ Hosp, Dept Obstet & Gynecol, Skejby, Denmark