The Effect of Low Oxygen Tension on the Early Development of Human Embryo in IVF/ICSI

Inclusion Criteria: * Fresh cycles of in vitro fertilization/intracytoplasmic sperm injection and emrbyo transfer (IVF/ICSI-ET) * ≥ 10 oocytes after oocyte retrieval Exclusion Criteria: * ≥ 3 transfer or oocyte retrieval cycles * PGD/PGS cycles * half-ICSI/rescure ICSI * fluid in the uterine cavity, abnormal endometrium, uterine abnormalities,pelvic inflammation * acute maternal problems. * One or both spouses have an abnormal karyotype (including polymorphism)