Vitrification and Blastocyst Transfer

Embryos were vitrified and thawed by using the conventional method. Blastocysts with a score of 3BB or better were considered to be high quality (Alpha Scientists in Reproductive and Embryology, 2011 (link)). High quality blastocysts were transferred under the guidance of ultrasound. No more than two cleavage-stage embryos or single blastocyst were transferred at one time. Estradiol valerate, intramuscular injection of progesterone oil 40 mg/d and dydrogesterone tablets (Duphaston, Abbott Biologicals B.V Netherlands, 10 mg, op, bid) were given after embryos transfer.