[1] Ziekenhuis Oost Limburg, Dept Obstet & Gynecol, B-3600 Genk, Belgium
[2] Hasselt Univ, Fac Med & Life Sci, Diepenbeek, Belgium
[3] Hasselt Univ, I BioStat, Diepenbeek, Belgium
[4] Maastricht Univ, Med Ctr, Dept Obstet & Gynecol, GROW Sch Oncol & Dev Biol, Maastricht, Netherlands
[5] Univ Utrecht, Med Ctr, Dept Obstet & Gynecol, Utrecht, Netherlands