Marja Visser1, Monique H Mochtar2, Fulco van der Veen2. 1. Academic Medical Centre, University of Amsterdam, Center for Reproductive Medicine, Meibergdreef 9, Amsterdam, Noord-Holland, 1105 AZ, The Netherlands. m.visser@amc.uva.nl. 2. Academic Medical Centre, University of Amsterdam, Center for Reproductive Medicine, Meibergdreef 9, Amsterdam, Noord-Holland, 1105 AZ, The Netherlands.