From the Research
For optimal frozen embryo transfer (FET) outcomes, progesterone levels should ideally be greater than 50 nmol/L and estrogen (estradiol) levels between 200-600 pg/mL (734-2202 pmol/L) on the day of transfer, as supported by the most recent and highest quality study 1.
Optimal Progesterone and Estrogen Levels
To achieve the best possible outcomes in frozen embryo transfer, it is crucial to maintain optimal levels of progesterone and estrogen. The ideal range for progesterone is above 50 nmol/L, as indicated by a study published in 2018 2, which demonstrated increased live birth rates and decreased pregnancy loss rates with day 16 serum progesterone concentrations greater than 50 nmol/L.
Estrogen Levels
Estrogen levels should be between 200-600 pg/mL (734-2202 pmol/L) to stimulate endometrial growth and receptivity to the embryo.
Progesterone Supplementation
Progesterone supplementation is typically administered for 5-6 days before a day-5 blastocyst transfer, using vaginal suppositories, intramuscular progesterone in oil, or a combination.
- The choice of progesterone formulation and dosage may impact outcomes, with intramuscular progesterone showing promising results in a 2021 study 3.
- Blood tests to check hormone levels are often performed the day before or morning of transfer to ensure optimal ranges.
- If levels are suboptimal, medication adjustments may be made to achieve the desired hormone levels.
Endometrial Preparation
The endometrial preparation method, whether natural or artificial, can also influence FET outcomes. A 2024 review 1 compared different endometrial preparation methods, highlighting the importance of supplementing with exogenous progesterone to ensure optimal obstetric outcomes.
- Letrozole is a recommended option for anovulatory patients, preserving endometrial thickness and being cost-effective and well-tolerated.
- A novel approach, the natural-proliferative-phase-FET, initiates progesterone in an unmediated ovulatory cycle at 7 mm endometrial thickness, combining the benefits of a natural proliferative endometrium with the convenience of scheduled artificial cycles.