Frozen Blastocyst Transfer Protocol

The blastocysts were thawed on the morning of FBT using a sequential dilution solution of sucrose, hatched by laser, and cultured for approximately 2 h until embryo transfer. Endometrial preparation was performed in two different ways. The natural cycle method was used for patients who had regular menstrual cycles with normal ovulation, and HCG was injected for triggering ovulation. In the artificial cycle method, oestradiol valerate (Progynova, Schering, Germany) was administered orally on days 2–4 of menstruation, and different starting doses (2–18mg/day) were given for the women on basis of their previous endometrial conditions. When the thickness of the endometrium reached 8 mm, progesterone (20mg×2d, 40mg×2d,20-40mg×1d) was injected intramuscularly for 5 days. On the 6th day, the blastocysts were thawed and transferred. Progesterone vaginal gel 8% (Crinone, Merck Serono, Feltham, UK) or intramuscularly ingested progesterone were used for luteal support.