The media used for embryo culture was IVF-60. Briefly, after oocyte retrieval (day 0), cumulus-enclosed oocytes were incubated in IVF-60. Semen was prepared with a 45-90 discontinuous gradient. The resulting pellet was washed in IVF-60. For normal IVF, 100,000 to 150,000 sperm/100ul were used for each oocyte. The maturation stage of oocyte was assessed for IVF 15-18 hour after insemination (day 1). Cumulus and corona cells were removed using drawn pipettes. When ICSI was performed, oocytes were denuded with HYASE. Each mature oocyte was placed in a 6-ul droplet of GAMETE-20. The partner's sperm was placed in a 6-ul droplet of ICSI-100. All droplets were overlaid with OVOIL. ICSI was performed using a inverted microscope with RI micromanipulators (INTEGRA Micromanipulation System, Research Instruments, UK). The CO2 incubators (Forma, USA) with 6% CO2 gas were used for embryo incubation. An embryo scoring system based on cleavage rate and morphologic features was used for the evaluation of embryo quality, as previously described elsewhere (9). Briefly, grade 1 is the best score and grade 5 is the worst. For example, a grade 1 embryo has blastomeres of equal size with no cytoplasmic fragmentation. A grade 2 embryo has symmetric blastomeres, but a small degree of cytoplasmic fragmentation involving ≤10% of the embryo's surface. Grades 3 through 5 demonstrate progressive embryo cytoplasmic fragmentation and variable cell symmetry.