Objective To assess the value of rescue intracytoplasmic sperm injection(ICSI) 5 hours post-insemination (hpi) with short co-incubation in in vitro fertilization-embryo transfer(IVF-ET). Methods Extrusion of the second polar body was observed 3, 4, and 5 hpi, and that oocytes extruded the second polar body were regarded as fertilization. If less than 65% of oocytes from 1 patient were observed to extrude the second polar body 5 hpi, the remaining oocytes with only the first polar body underwent rescue ICSI. 1050 patients who received IVF were divided into group Ⅰ: partly receiving rescue ICS I, and group Ⅱ: without rescue ICSI. Oocytes in group Ⅰwere divided into rescue ICSIoocytes and only IVF oocytes. 201 patients in the control group received ICSI. Results ① The rates of oocytes which extruded the second polar body 3, 4, and 5 hpi in groupⅠ were all lower than those in group Ⅱ(P<0.05), and the rates of primary infertility and unexplained infertility in groupⅠ were higher than those in groupⅡ(P<0.05). ② No difference existed in fertilization rate, poly-spermic rate, clinical pregnancy rate, and implantation rate among rescue ICSI oocytes in groupⅠ,the control group, and groupⅡ(P>0.05). The rate of high quality embryo oriented from rescue ICSI oocytes in groupⅠ was lower than that in group Ⅱ and the control group(P<0.05). Conclusions Gamete co-incubation for 3h is feasible in IVF. Extrusion of the second polar body 5 hpi is regarded as fertilization. Early rescue ICSI 5 hpi results in satisfactory clinical outcomes, while the poly-spermic rate is not increased. Primary infertility and unexplained infertility are liable to have a low fertilization rate.
