Ovarian stimulation protocol, endometrial preparation protocol, ET process, and luteal support
A personalized controlled ovarian hyperstimulation (COH) protocol was chosen for each patient according to her age, anti-Müllerian hormone level, body mass index (BMI), number of antral follicles in the bilateral ovaries, and prior response to stimulation13-15. Follicular development was determined by transvaginal ultrasonography, and the dosages of gonadotropin were adjusted according to different ovarian responses.
When the follicles reached a diameter of more than 17 mm, the trigger was performed for final oocyte maturation. Oocyte retrieval was performed 36 hours after triggering with transvaginal ultrasound-guided aspiration.
Endometrial preparation for FET used the HRT cycle, wherein 4-8 mg of estradiol valerate (Progynova, Bayer, Germany) was administered orally for at least 10 days from the 3rd to 5th days of menstruation to promote endometrial growth. The cut-off value for endometrial transformation was more than 8 mm. The embryos were slowly injected 10 mm from the uterine fundus under ultrasound guidance, and the catheter remained in situ for 3-5 seconds. The patients subsequently stood upright and walked to the rest area, where they lay in bed for 20-30 min before leaving.
The luteal phase was supported by vaginal administration of progesterone gel (Crinone, Fleet Laboratories Ltd., UK) at 90 mg/day, while estradiol was maintained at the original dose. Luteal support was continued until 11 weeks of gestational age.