OBJECTIVETo study the impact of postovulatory ageing to balanced predivision of oocyte sister chromatid.

METHODSThe mouse oocytes were cultured 0-72 h. Then chromosome 16 was detected by fluorescence in situ hybridization (FISH). The oocyte spindle and chromosome configuration were examined by immunocytochemistry.

RESULTSFor freshly ovulated mouse oocyte, the balanced predivision of sister chromatid occurred only at 7%. However, for oocytes cultured for 24 h, 48 h and 72 h in vitro, the balanced predivision of sister chromatid occurred up to at 32%, 51% or 62% respectively (P< 0.01). The abnormal cell spindle and chromosome configuration occurred at 9% of freshly ovulated oocytes, but it increased to 63%, 83% and 98% when the oocytes were cultured in vitro for 24 h, 48 h or 72 h respectively (P< 0.01).

CONCLUSIONThe occurrence of balanced predivision of oocyte sister chromatid may result during postovulatory ageing, and may be related to change of oocyte spindle and chromosome configuration.