PRELIMINARY-OBSERVATIONS ON POLAR BODY EXTRUSION AND PRONUCLEAR FORMATION IN HUMAN OOCYTES USING TIME-LAPSE VIDEO CINEMATOGRAPHY

In this study, we have used time-lapse video cinematography to study f ertilization in 50 human oocytes that had undergone intracytoplasmic s perm injection (ICSI), Time-lapse recording commenced shortly after IC SI and proceeded for 17-20 h, Oocytes were cultured in an environmenta l chamber which was maintained under standard culture conditions, Over all, 38 oocytes (76%) were fertilized normally, and the fertilization rate and embryo quality were not significantly different from 487 sibl ing oocytes cultured in a conventional incubator, Normal fertilization followed a defined course of events, although the timing of these eve nts varied markedly between oocytes. In 35 of the 38 fertilized oocyte s (92%), there were circular waves of granulation within the ooplasm w hich had a periodicity of 20-53 min, The sperm head decondensed during this granulation phase, The second polar body was then extruded, and this was followed by the central formation of the male pronucleus, The female pronucleus formed in the cytoplasm adjacent to the second pola r body at the same time as, or slightly after, the male pronucleus, an d was subsequentry drawn towards the male pronucleus until the two abu tted, Both pronuclei then increased in size, the nucleoli moved around within the pronuclei and some nucleoli coalesced, During pronuclear g rowth, the organelles contracted from the cortex towards the centre of the oocyte, leaving a clear cortical zone, The oocyte decreased in di ameter from 112 to 106 mu m (P < 0.0001) during the course of the obse rvation period, The female pronucleus was significantly smaller in dia meter than the male pronucleus (24.1 and 22.4 mu m respectively, P = 0 .008) and contained fewer nucleoli (4.2 and 7.0 respectively, P < 0.00 01), After time-lapse recording, oocytes were cultured for 48 h prior to embryo transfer or cryopreservation, Embryo quality was related to fertilization events and periodicity of the cytoplasmic wave, and it w as found that good quality embryos arose from oocytes that had more un iform timing from injection to pronuclear abuttal and tended to have a longer cytoplasmic wave, In conclusion, we have shown that time-lapse video cinematography is an excellent tool for studying fertilization and early embryo development, and have demonstrated that human fertili zation comprises numerous complex dynamic events.