Fertilization and pregnancy using metaphase I oocytes in an intracytoplasmic sperm injection program

Purpose: In this study we investigated whether metaphase I oocytes collected in an intracytoplasmic sperm injection program could successfully be matured and fertilized by injecting aged (>20-hr) spermatozoa. Materials and Methods: Metaphase I oocytes aspirated were preincubated for 20 hr to allow the oocytes to reach meiotic maturity. Only metaphase II oocytes were injected. The original sperm sample processed on the day of aspiration was used in the microinjection process. Results: One hundred eighty-three oocytes were collected, of which 42 (23%) were metaphase I oocytes. These were incubated for 20 hr and microinjected with the original sperm sample. Thirty-one (74%) of the metaphase I oocytes reached meiotic maturity (extruded polar body); 67.7% showed two pronuclei 18 hr after injection and 61.3% embryo development 40 hr postinjection. No difference in fertilization and embryo development rate was found in metaphase II oocytes injected 6 hr postaspiration versus 20 hr postaspiration. An ongoing pregnancy was also achieved using only embryos obtained from matured metaphase I oocytes. Conclusions: Metaphase I oocytes can be successfully maturedin vitro and injected using aged (>20-hr) sperm samples. Matured metaphase I oocytes, if successfully injected, produce embryos able to induce pregnancy.