Endometrial preparation and embryo transfer
PROLIFERATIVE
All cycles were performed using the same artificial protocol. Oral estradiol valerate (Progynova, BayerSchering Pharma AG, Germany) was administered on the second or third day of the menstrual cycle after verifying that the patients were in the early proliferative phase of the menstrual cycle. Typically, 3 mg of estradiol valerate was prescribed twice daily. If the endometrial thickness was <7 mm 14 days later, patients were required to comply with a step-up protocol that involved the addition of vaginal estrogen supplementation (Femoston, Abbott Healthcare Products; 1 mg once daily), to the oral administration of estradiol valerate, based on the physician’s preference and experience. Serum estradiol and progesterone levels were determined on the day before the initiation of progesterone treatment.Intramuscular progesterone (60 mg once a day) was initiated, supplemented with oral dydrogesterone (10 mg thrice a day) when the endometrial thickness was 7 mm. Embryo transfer was performed days 4, 5, 6 and 7 of progesterone exposure in groups P3, P4, P5 and P6 respectively. No more than two embryos were transferred in any FET cycles. All the embryos were thawed on the morning of the transfer. Embryos were evaluated according to the conventional classification system currently used in our IVF laboratory: number of blastomeres, degree of cytoplasmic fragmentation and the equality of blastomeres (