Fertilization and embryo evaluation
Semen samples were prepared by the swim-up procedure. About 2 hours
after oocyte retrieval, each oocyte was inseminated with approximately
20,000–30,000 motile spermatozoa. If the total number of motile sperm
was <105 after washing or normal morphology
was <1%, intracytoplasmic sperm injection (ICSI) was
performed. Oocytes were decoronated and checked for the presence of two
pronuclei to confirm fertilization. Embryos were graded on day 3 after
retrieval as grade one to grade six according to the evenness of each
blastomere and the percentage of fragmentation. Embryos of 6-8 cells and
of grade one or two were regarded
as
top quality embryos.
Some non-top-quality embryos were
placed in extended culture until they reached the
blastocyst stage.