Early development of in vitro aged eggs after intracytoplasmic sperm injection

Recently, rescue approaches for eggs that failed to be fertilized using intracytoplasmic sperm injection (ICSI) have been addressed (rescue ICSI). We believe that target eggs for rescue ICSI have already aged by the time they are reinseminated; therefore, they are essentially different from fresh, unfertilized eggs. This study examined the development of embryos derived from eggs aged in vitro after ICSI. It was observed that in vitro aging for 12 h or more causes an abnormality of the cleavage apparatus in metaphase II eggs. This abnormality leads to various disabilities such as impairment of fertilization and early development, numerical chromosome aberration, and reduced blastomeres.