Preincubation of human oocytes may improve fertilization and embryo quality after intracytoplasmic sperm injection

The aim of this study was to examine the relationship between different preincubation periods of oocytes and the outcome of intracytoplasmic sperm injection (ICSI), We analysed retrospectively 95 ICSI treatment cycles performed to alleviate severe male-factor infertility, Oocyte collection was performed similar to 36 h after human chorionic gonadotrophin administration. The cumulus-corona-oocyte complexes obtained were incubated until the moment of ICSI, Fertilization, embryo development and implantation rates were analysed in four groups, which were divided according to the time lapse between oocyte retrieval and ICSI: group I, less than or equal to 3 h (18 cycles); group II, >3-less than or equal to 6 h (52 cycles); group III, >6-less than or equal to 9 h (14 cycles); and group IV, >9-less than or equal to 12 h (11 cycles). Immediately before ICSI the cumulus and corona cells were removed from the oocytes, ii total of 723 metaphase II oocytes were injected: 126 from group I, 380 from group II, 126 from group III and 91 from group IV. The fertilization rates obtained were 52.3, 66,8, 65.1 and 69.2% respectively [P < 0.05 (using the chi(2) test) between group I and groups II, m and IV]. Cleavage rates were similar in all groups (68.1, 69.7, 79.2 and 79.3% respectively), but the proportion of good quality embryos (less than or equal to 20% fragmentation) was significantly lower (P < 0.05) in group I (24.2%) compared with groups II (39.8%) and IV (39.6%). However, no statistically significant differences were observed between the four,groups with regard to implantation rates (11.7, 13.2, 10.4 and 20.4% respectively). results suggest that a preincubation period between re retrieval and ICSI can improve the fertilization rate Id embryo quality. This period might be necessary for me oocytes to reach full cytoplasmic maturity, leading to higher activation rate upon microinjection.