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 total number of motile sperm was
<105 after washing or normal morphology was
<4%, 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 fragmentation13. 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.