Human Reproduction, Vol. 17, No. 9, 2394-2401,
September 2002
© 2002 European Society of Human Reproduction and Embryology
Morphological and cytogenetic analysis of human giant oocytes and giant embryos*
1 CReATe Program, Inc. and 2 Department of Obstetrics and Gynecology, Sunnybrook and Women's College Health Sciences Center, University of Toronto, Toronto and the 3 University Health Network and Department of Laboratory Medicine and Pathobiology, and Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Canada
BACKGROUND: Giant binuclear oocytes occur with considerable frequency in human ovaries, but their ultimate fate remains unknown. We report the morphology, cytogenetics and developmental potential of human giant oocytes from patients undergoing assisted reproductive technologies. METHODS AND RESULTS: A total of 44 giant oocytes was collected from patients aged 22–44 years old, with an overall frequency of 0.3% (44/14 272 oocytes). Giant oocytes were ~30% larger in diameter than normal oocytes (mean 200.4 versus 154.7 µm, P = 0.0001). Two different morphological patterns were observed among giant unfertilized and fertilized oocytes. All unfertilized oocytes appeared to be diploid and contained either one or two metaphase plates (46 or 2x23 chromosomes), and one or two polar bodies respectively. Consequently, fertilized giant oocytes exhibited either two or three pronuclei, or two or four polar bodies. Both types of giant zygotes were capable of normal cleavage and development to blastocyst stage. Four giant embryos were analysed by interphase fluorescence in-situ hybridization using probes for chromosomes 9, 22, X and Y, and all appeared chromosomally abnormal with numerical alterations indicative of ploidy change. CONCLUSIONS: Giant oocytes might be a possible source of human digynic triploidy. To avoid undesired miscarriages, giant embryos originated from either two- or three-pronuclear giant zygotes should be excluded from uterine transfers.
Key words: digynic triploidy/digyny/diploid oocytes/human triploidy/ploidy
* The results of this study were presented at the 57th Annual Meeting of the ASRM, Orlando, Florida, USA, 2001.
4 To whom correspondence should be addressed at: CReATe (Canadian Reproductive Assisted Technology) Program, Inc., 790 Bay Street, suite 1020, Toronto, Ontario M5G 1N8, Canada. E-mail: hbalakier{at}sympatico.ca
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