Correlation between oocyte preincubation time and pregnancy rate after intracytoplasmic sperm injection

Background and aim. Both nuclear and cytoplasmic maturation of oocytes have to be completed in a coordinated manner to ensure optimal conditions for fertilization. This is well known for in vitro fertilization, but is debated for intracytoplasmic sperm injection (ICSI). It has been reported that preincubation of oocytes prior to ICSI is associated with improved maturation of oocytes, fertilization and embryo quality. Therefore, in the present study, we evaluated the fertilization rate, embryo quality and pregnancy rate in relation to incubation times of metaphase-II oocytes before ICSI.

Method. We analyzed 135 selected ICSI cycles. Subjects were assigned to six groups according to oocyte incubation time before ICSI: 2–4 h, 5 h, 6 h, 7 h, 8 h and 9–12 h.

Results. We observed that the fertilization rate increased slightly at short (2 to 6 h) and then decreased at longer preincubation times (7 to 12 h). Concomitantly, cleavage rate increased up to 6 h of preincubation and decreased significantly in the groups in which ICSI was carried out after 7 to 12 h of incubation. With regard to clinical pregnancy rate, we observed a significant increase from 2 to 5 h of preincubation, when this parameter reached its maximum value (35%), tapering to 33% after 6 h and then dropping sharply to 12 h.

Conclusions. These data confirm that the most appropriate incubation time for mature oocytes before ICSI is 5–6 h. This time improves embryo quality and pregnancy rate in ICSI cycles.