Embryo transfer protocol and luteal support
Fresh embryo transfer: The ovulation induction protocol was chosen according to the clinical characteristics of the patients. When the dominant follicle diameter was ≥ 17 mm, recombinant human chorionic gonadotropin (hCG) was injected, and ultrasound-guided transvaginal oocyte retrieval was performed 36-38 hours after the injection.
HRT-FET cycle: For women with a previous history of a thin endometrium or an irregular menstrual cycle, oral oestradiol valerate (Progynova, Schering, Germany) 4-6 mg/d was administered from day 3 of menstruation, and the dose was adjusted according to endometrial thickness. When endometrial thickness reached 8 mm or more (with oestradiol valerate continued for at least 10-12 days), progesterone gel (Serotonin, Merck Serono, 90 mg/d) combined with dydrogesterone tablets (Duphaston, Solvay Netherlands, 10 mg bid in the first two days, 20 mg bid later) was administered prior to endometrial transformation. The Day 3 cleavage embryo or the Day 7 blastocyst was thawed and transferred.
NC-FET cycle: For patients with regular menstrual cycles, ovulation was monitored by transvaginal ultrasound, and cleavage-stage embryos were transferred on the 3rd day after ovulation, whereas blastocysts were transferred on the 5th day after ovulation. Dydrogesterone tablets (Duphaston, Solvay Netherlands, 20-40 mg/d) were taken from the day of ovulation until the 12th-14th day after embryo transfer.
After fertilization, the cleavage and development of embryos were evaluated. Embryos available for transfer contained 4-8 blastomeres on the 3rd day after fertilization and were graded 2 or above. No more than 2 emtryos could be transferred and the remaining embryos were cryopreserved. Embryos with more than 50% viable cells after thawing could be transferred. The level of β-hCG in serum was checked on the 12th-14th day after embryo transfer. The appearance of an intrauterine gestational sac in vaginal ultrasonography performed 4 weeks after embryo transfer was diagnosed as clinical pregnancy. Progesterone gel (Serotonin, Merck Serono, 1 time/d, 90 mg/d) was used for luteal support, fresh embryo transfer and natural cycle medications were administered until the 8th-10th week of pregnancy, and the artificial cycle was performed until the 12th week of pregnancy.