Department of Obstetrics and Gynecology, University of Groningen, University Medical Centre Groningen, 9700 RB Groningen, The Netherlands. Department of Epidemiology, University of Groningen, University Medical Centre Groningen, 9700 RB Groningen, The Netherlands. Department of Public and Occupational Health, Amsterdam University Medical Centre, Vrije Universiteit Amsterdam, De Boelelaan 1117, 1105 AZ Amsterdam, The Netherlands. Department of Clinical Epidemiology, University of Amsterdam, Amsterdam University Medical Centre, Biostatistics and Bioinformatics, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Department of Obstetrics and Gynecology, University of Amsterdam, Amsterdam University Medical Centre, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Amsterdam Public Health Research Institute, 1105 AZ Amsterdam, The Netherlands. Amsterdam Reproduction and Development, 1105 AZ Amsterdam, The Netherlands. Department of Obstetrics and Gynecology, Monash University, Melbourne 3800, Australia.