[1] Univ Groningen, Univ Med Ctr Groningen, Dept Gynaecol, POB 30-001, NL-9700 RB Groningen, Netherlands
[2] Martini Hosp Groningen, Dept Obstet & Gynaecol, Groningen, Netherlands
[3] Maxima Med Ctr Veldhoven, Dept Obstet & Gynaecol, Veldhoven, Netherlands
[4] Hosp Grp Twente Almelo, Dept Obstet & Gynaecol, Med Spectrum Twente Enschede, Hengelo, Netherlands
[5] Wilhelmina Hosp Assen, Dept Obstet & Gynaecol, Assen, Netherlands
[6] Nij Smellinghe Hosp Drachten, Dept Obstet & Gynaecol, Assen, Netherlands
[7] Rijnstate Hosp Arnhem, Dept Obstet & Gynaecol, Arnhem, Netherlands
[8] Med Ctr Leeuwarden, Dept Obstet & Gynaecol, Leeuwarden, Netherlands
[9] Maastricht Univ, Dept Obstet & Gynaecol, Med Ctr, Maastricht, Netherlands
[10] Antonius Hosp Sneek, Dept Obstet & Gynaecol, Sneek, Netherlands
[11] Leiden Univ, Dept Gynaecol, Med Ctr, Leiden, Netherlands
[12] Onze Lieve Vrouwe Gasthuis Amsterdam, Dept Gynaecol, Amsterdam, Netherlands
[13] Amsterdam Univ Med Ctr, Dept Gynaecol, Amsterdam, Netherlands
[14] VieCuri Med Ctr Venlo, Dept Obstet & Gynaecol, Venlo, Netherlands
[15] Univ Groningen, Univ Med Ctr Groningen, Dept Epidemiol, Groningen, Netherlands