Blastocyst Transfer Timing After Progesterone Initiation
Blastocyst transfer should be performed on day 5 or day 6 after starting progesterone supplementation, with the optimal timing being 117-120 hours (approximately 5 days) after the first progesterone dose. 1
Standard Protocol for Frozen Blastocyst Transfer
The timing of blastocyst transfer is calculated from the first progesterone dose and follows a precise schedule 1:
- Day 5 blastocysts: Transfer on day 5 of progesterone (120 hours after progesterone initiation) 2, 3
- Day 6 blastocysts: Transfer on day 6 or day 7 of progesterone, with day 7 showing superior outcomes 4, 3
Evidence-Based Timing Recommendations
For Day 5 Blastocysts
Transfer on the 5th day of progesterone administration yields optimal outcomes. 2, 3 Recent evidence demonstrates that day 5 blastocysts transferred on day 5 versus day 6 of progesterone show comparable pregnancy outcomes, though the 5-day protocol is standard 3.
For Day 6 Blastocysts
Transfer on the 7th day of progesterone is strongly preferred over the 6th day for day 6 blastocysts. 4, 3 This recommendation is based on:
- Significantly higher live birth rates (44.8% vs 36.4%) when transferred on day 7 versus day 6 of progesterone 3
- Lower pregnancy loss rates (15.4% vs 25.2%) with the 7-day protocol 3
- Markedly reduced miscarriage rates (21.4% vs 50.0%) when day 6 blastocysts are transferred on day 7 versus day 6 of progesterone 4
Critical Pre-Transfer Requirements
Before initiating progesterone, the following must be confirmed 1, 5:
- Estrogen priming duration: Continue estradiol (Progynova 6mg daily) for 12-14 days minimum before starting progesterone 1, 5
- Endometrial thickness: ≥7-8mm with trilaminar pattern on ultrasound 1, 5
- Adequate endometrial preparation: Confirmed via transvaginal ultrasound on day 12-14 of the cycle 5
Common Pitfalls to Avoid
Never start progesterone on a fixed cycle day without confirming adequate endometrial preparation. 1 The most critical error is initiating progesterone prematurely (e.g., on cycle day 9) without ensuring 12-14 days of estrogen exposure, which risks poor implantation outcomes 1.
Do not transfer day 6 blastocysts on day 6 of progesterone. 4, 3 This timing is associated with a 50% miscarriage rate compared to 21.4% when transferred on day 7 of progesterone 4.
The Implantation Window
The window for successful embryo transfer depends critically on progesterone duration 6:
- Opens approximately 48 hours (2 days) after starting progesterone 6
- Remains open for approximately 4 days 6
- Optimal transfer occurs on days 18-19 of an artificial cycle (corresponding to 4-5 days of progesterone for cleavage-stage embryos) 6
For blastocysts specifically, this translates to day 5-6 of progesterone for day 5 blastocysts and day 6-7 for day 6 blastocysts, with day 7 being superior for the latter 4, 3.