What is the best protocol for endometrial preparation for vitrified donor oocyte thaw?

From 1/1/22 through 4/15/25 our center has performed 88 single day 5 fresh embryo transfers after vitrified donor oocyte thaw and ICSI. We have patients start oral estradiol 2mg three times a day on menses cycle day 1-3 and then do transvaginal ultrasound and check estradiol and progesterone on cycle day 12 to 16. Most commonly we see patients on cycle day 12.

We aim for a trilaminar endometrium with thickness of 7.0mm or greater. If the endometrium is thin we typically add vaginal estradiol 2mg daily and see them back in 4-7 days for a repeat lining check. Once the lining is appropriate we start progesterone in 1 to 4 days and transfer on the 6th day of progesterone. We typically thaw oocytes in the morning and then start progesterone the same day in the evening. We use Prometrium 200mg vaginally 3 times a day (TID) or Endometrin 100mg vaginally TID. For patients also taking progesterone in oil (PIO) we add 50mg PIO IM every 3 days. We use Endometrin approximately 25% of the time and Prometrium 75% of the time. We see no differences between Endometrin and Prometrium.

We define an ongoing pregnancy as a fetal heartbeat detected at or after 8 weeks 0 days gestation and no report to our clinic of a spontaneous abortion by 14 weeks 0 days gestation.

Our most common protocol is Vaginal Progesterone TID and PIO 50mg IM Every 3 days which resulted in an ongoing pregnancy rate of 52% per single embryo transfer.

Our next most common protocol was Vaginal Progesterone TID which resulted in an ongoing pregnancy rate of 58% per single embryo transfer.