Patients undergoing routine IVF, following informed consent, donated some of their unusable, immature- MI stage oocytes for our research. Following in vitro maturation for up to 2, 4, 8 and 24 hours after harvest, all immature oocytes in these 4 study groups underwent intracytoplasmic donor sperm injection (ICSI), whether they extruded their polar body (MI-PB or rescued MI) or not (arrested MI). Oocyte fertilization rate after 24 hours and embryonic development in terms of cleavage rate and morphology were assessed, for another 48 hours. Then the whole embryo was prepared for molecular cytogenetic evaluation using FISH (Fluorescence in situ hybridization) analysis of chromosomes x, y and 18.