Objectives: Recently, advances have been made to treat women with polycystic ovarian syndrome (PCOS)-related infertility by in-vitro maturation (IVM) technology. Unlike the embryos resulting from IVF/ICSI cycles, embryos produced by IVM originate from immature oocytes, which had been recovered in the absence, or with limited gonadotrophic exposure, and then matured in-vitro prior to insemination. The incidence of chromosome abnormalities in preimplantation embryos produced via IVM is unknown. The aim of this study is to investigate the chromosomal constitution of spare preimplantation embryos obtained from IVM cycles using fluorescence in-situ hybridization (FISH) with chromosome specific DNA probes.Materials and Methods: All embryos originated from oocytes donated by patients with polycystic ovaries or PCOS. The mean patient age was 31.3 years (range 25–39 years). Immature oocytes had been recovered on day 10–14 of the cycles, either in absence of gonadotrophins, or with HCG priming (10 000IU) 36 h before oocyte retrieval. Oocytes had been cultured in-vitro to maturation for 12–48 h, and fertilized by ICSI. Blastomeres from fertilized 2-cell to 8-cell stage, mostly grade-III to grade-IV embryos, were spread by the HCl/Tween 20 method. Nuclei were treated with pepsin and dehydrated. Nuclei were hybridized with fluorescently labelled DNA probes specific to chromosomes X, Y, 18 and/or chromosomes 13, 16, 18, 21, 22 and analyzed for the presence of numerical chromosomal abnormalities.Results: Up to date, a total of 31 IVM embryos have been analyzed by FISH. Thirteen percent of embryos were diploid, 22% were polyploid, 26% were chaotic with blastomeres of variable chromosome patterns, and 39% percent of embryos were mosaic, consisting of both, chromosomally normal and abnormal cells. Interestingly all the polyploid embryos were triploid (3N), with XXX or XXY chromosome complements.Conclusions: Preliminary results suggest that, similar to embryos produced by conventional IVF/ICSI, embryos from IVM cycles have a high incidence of chromosome abnormalities. Our results suggest that the high incidence of 3N embryos from IVM cycles may be a consequence of increased rates of diploidy among in-vitro matured oocytes. Examination of a much larger number of IVM generated embryos is necessary to determine whether these findings have important clinical implications. Objectives: Recently, advances have been made to treat women with polycystic ovarian syndrome (PCOS)-related infertility by in-vitro maturation (IVM) technology. Unlike the embryos resulting from IVF/ICSI cycles, embryos produced by IVM originate from immature oocytes, which had been recovered in the absence, or with limited gonadotrophic exposure, and then matured in-vitro prior to insemination. The incidence of chromosome abnormalities in preimplantation embryos produced via IVM is unknown. The aim of this study is to investigate the chromosomal constitution of spare preimplantation embryos obtained from IVM cycles using fluorescence in-situ hybridization (FISH) with chromosome specific DNA probes. Materials and Methods: All embryos originated from oocytes donated by patients with polycystic ovaries or PCOS. The mean patient age was 31.3 years (range 25–39 years). Immature oocytes had been recovered on day 10–14 of the cycles, either in absence of gonadotrophins, or with HCG priming (10 000IU) 36 h before oocyte retrieval. Oocytes had been cultured in-vitro to maturation for 12–48 h, and fertilized by ICSI. Blastomeres from fertilized 2-cell to 8-cell stage, mostly grade-III to grade-IV embryos, were spread by the HCl/Tween 20 method. Nuclei were treated with pepsin and dehydrated. Nuclei were hybridized with fluorescently labelled DNA probes specific to chromosomes X, Y, 18 and/or chromosomes 13, 16, 18, 21, 22 and analyzed for the presence of numerical chromosomal abnormalities. Results: Up to date, a total of 31 IVM embryos have been analyzed by FISH. Thirteen percent of embryos were diploid, 22% were polyploid, 26% were chaotic with blastomeres of variable chromosome patterns, and 39% percent of embryos were mosaic, consisting of both, chromosomally normal and abnormal cells. Interestingly all the polyploid embryos were triploid (3N), with XXX or XXY chromosome complements. Conclusions: Preliminary results suggest that, similar to embryos produced by conventional IVF/ICSI, embryos from IVM cycles have a high incidence of chromosome abnormalities. Our results suggest that the high incidence of 3N embryos from IVM cycles may be a consequence of increased rates of diploidy among in-vitro matured oocytes. Examination of a much larger number of IVM generated embryos is necessary to determine whether these findings have important clinical implications.