[1] Univ Southern Denmark, Fac Hlth Sci, Dept Publ Hlth, Res Unit Gen Practice, JB Winslews Vej 9B, DK-5000 Odense C, Denmark
[2] Univ Hosp Zealand, Dept Gynaecol & Obstet, Roskilde, Denmark
[3] Univ Southern Denmark, Fac Hlth Sci, Dept Clin Res, Res Unit Gynaecol & Obstet, Odense C, Denmark
[4] Karolinska Univ Sjukhuset, Dept Womens & Childrens Hlth, Div Obstet & Gynecol, Stockholm, Sweden
[5] Univ Hosp Odense, Dept Gynaecol & Obstet, Odense C, Denmark
[6] Univ Southern Denmark, Fac Hlth Sci, Natl Inst Publ Hlth, Copenhagen, Denmark