Nuclear degeneration and meiotic aberrations observed in human oocytes matured in vitro: analysis by light microscopy

Abstract

To apply an improved air-dry procedure for the light microscopic identification of both degenerate and aberrant meiotic configurations in cultured human oocytes. MATERIAL AND DESIGN: Meiotically immature, normal appearing human oocytes retrieved after oophorectomy were placed into culture for 9 to 46 hours. Subsequently, oocytes were assessed morphologically and then air dried for light microscopic examination of chromatin configurations. Oocyte chromatin configurations were identified as normal, degenerate, or aberrant and then classified according to meiotic stage. Retrospective analyses were conducted to determine if [1] normal meiotic configurations were associated with morphologically viable oocytes and [2] degenerate or aberrant meiotic configurations were always associated with degenerate oocytes. In addition, for each meiotic stage, the proportion of oocytes exhibiting either degenerate or aberrant chromatin configurations was calculated. Of 101 oocyte chromatin configurations analyzed, 71.3% were normal, 11.9% were degenerate, and 16.8% displayed meiotic aberrations. Retrospective analyses revealed that the majority of both normal and aberrant chromatin configurations were associated with morphologically viable oocytes (93.1% and 88.2%, respectively), whereas all of the degenerate chromatin configurations were associated with morphologically degenerate oocytes. When assessed by stage, nuclear degeneration was observed exclusively at the germinal vesicle and diakinesis stages, whereas meiotic aberrations occurred most frequently after chromosome condensation. These aberrations were manifested either as clumped metaphase I configurations or as two distinct groups of bivalents that appeared to result from bivalent migration along the meiotic spindle without homologue segregation. Slightly > 25% of human oocytes recovered after oophorectomy were incapable of undergoing normal meiotic maturation in culture. The majority of these abnormal oocytes appeared morphologically normal and yet possessed meiotic aberrations. These observations indicate that caution should be taken when using oocytes matured in vitro for application in assisted reproductive technology programs.