Fresh or Frozen?
By Francis Polansky, M.D.
There is no difference in a probability of a live birth between “fresh” and frozen embryo transfers in the IVF treatment.
In Vitro Fertilization embryos are transferred inside the uterus either as fresh on day #5 of their development or as frozen-thawed in a subsequent cycle of treatment. This choice depends on several factors.
For an embryo to successfully implant, its development must match perfectly with the development of the endometrial lining. After egg retrieval, eggs are inseminated with sperm, and the following day, the eggs that fertilized are classified as day #1 embryos. By day #5, optimally developing embryos should reach the blastocyst stage consisting of 80 to 100 cells.
To be a candidate for fresh embryo transfer, there must be at least one blastocyst available for embryo transfer on the morning of day #5. If it takes six or seven days for embryos to reach the blastocyst stage, they can still result in a live birth, but their development is now out of synchrony with the development of the endometrial lining.
If there is no day#5 blastocyst, all normally developing embryos are cryopreserved on day #6 or #7 and are then transferred in a subsequent cycle of frozen embryo transfer treatment.
Another reason for no fresh embryo transfer is estrogen or progesterone levels that are too high during IVF ovarian stimulation. High levels of these two hormones will cause the endometrial lining to be developing ahead of embryonic development.
Yet another cause of no fresh transfer is an endometrial lining which is too thin. This could significantly reduce the likelihood of embryo implantation. Endometrial lining stimulation as a part of the frozen embryo transfer will be needed for better endometrial lining development.
The final reason for having to freeze all normally developing embryos is too many follicles developing within the ovaries. Under such circumstances, the risk of severe ovarian hyperstimulation would be unacceptably high if there is a conception from a fresh embryo transfer.