1Department of Obstetrics/Gynecology 791, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, Netherlands
2Division of Obstetrics and Gynaecology, Department of Clinical and Experimental Medicine, Faculty of Health Sciences, Linköping University, SE-581 85, Linköping, Sweden
3Municipal Public Health Service Rotterdam-Rijnmond, Schiedamsedijk 95, Rotterdam 3011 EN, Netherlands
4Ladulaas Kliniska Studier, Industrigatan 2, SE-511 62 Skene, Sweden
5GlaxoSmithKline Biologicals, Wavre, Belgium