Protocol for Ovarian stimulation
Controlled ovarian stimulation was performed using the routine long GnRH agonist protocol. Oocytes were retrieved transvaginally 34–36 h after human chorionic gonadotropin (hCG) administration, and fertilization was assessed 16–18 h after routine insemination or ICSI. Blastomere number and regularity, as well as the presence and volume of cytoplasmic fragmentation, were assessed 24 and 48 h later, respectively. According to the protocol developed by Chinese legislation, no more than two embryos were transferred on day 3 or 5 after oocyte retrieval. The remaining available embryos were cultured for blastocyst formation. Then, all patients received luteal support after embryo transfer, including intramuscular injections of progesterone in oil or vaginally administered micronized progesterone.