Analysis of human unfertilized oocytes and pronuclear zygotes—Correlation between chromosome/chromatin status and patient-related factors Ralitsa S. Zhivkova a, * , Stefka M. Delimitreva a , Draga I. Toncheva b , Ilya T. Vatev a a IVF-ET Center, Department of Biology, Medical Faculty, Medical University Sofia, 1, St. Georgy Sofiisky Street, Sofia 1413, Bulgaria b Department of Medical Genetics, Medical Faculty, Medical University, Sofia, Bulgaria Received 17 August 2004; received in revised form 16 February 2006; accepted 12 March 2006 Abstract Objective: The objective was to evaluate the relationship between ploidy and chromatin status of human unfertilized oocytes/zygotes and infertility history, female age, and stimulation regimens. Study design: Two hundred and eighty-nine unfertilized oocytes and 63 zygotes were subjected to cytogenetic analysis: karyotyping for oocytes and fluorescent in situ hybridization (FISH) analysis for zygotes. Ploidy and chromosome/chromatin status were analyzed according to stimulation regimen, female age, and infertility history. The correlation coefficient was estimated and data were interpreted using a five- grade scale. Results: Aneuploidy in karyotyped oocytes (19.7% hyperhaploidy, 18.8% hypohaploidy, and 6.3% haploid abnormal) was associated with chromosome fragmentation and lesions due to chromosome aging in culture. Premature chromosome condensation and cytoskeletal defects were significantly higher in unexplained infertility (34.7% and 52.9%, respectively; p < 0.05). Chromatin quality was most important for successful ploidy analysis of zygotes. FISH analysis of abnormal zygotes elucidated genetic aspects of pronuclear number aberrations and raised questions about the current selection criteria. Abnormalities were found to correlate moderately with stimulation strategy and female age and significantly with infertility history. Conclusion: Genetic analysis of human oocytes and zygotes showed that poor chromatin quality and patient-related factors contribute to aneuploidy and pronuclear number aberrations. # 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Oocyte karyotype; Fluorescent in situ hybridization (FISH); Pronuclear number; Infertility; Ovarian stimulation; Age 1. Introduction The role of aneuploidy for pre- and post-implantation embryonic death is well documented and widely discussed in respect of the effectiveness of IVF-ET (in vitro fertilization and embryo transfer) procedures for family infertility treatment. Different clinical and biological factors have been studied to clarify the origin of aneuploidy in human gametes and preimplantation embryos. Classical and molecular cytogenetics have been used to investigate IVF failure. Variable aneuploidy rates in human oocytes, ranging from 8% to nearly 60%, have been cited [1,2] in the last decades and it is currently thought that aneuploidy in oocytes is due to imperfect control of female meiosis events and their synchronization with follicular growth. Generally accepted is the theory that maternal meiosis I errors are responsible for almost all aneuploidies. Non- disjunction of bivalent chromosomes and premature chromatid separation (meiosis I defects) have been www.elsevier.com/locate/ejogrb European Journal of Obstetrics & Gynecology and Reproductive Biology 130 (2007) 73–83 * Corresponding author. Tel.: +359 2 91 72 678; fax: +359 2 851 8631. E-mail address: zhivkova@medfac.acad.bg (R.S. Zhivkova). 0301-2115/$ – see front matter # 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ejogrb.2006.03.022