If more eggs are normally fertilized and divide to form healthy-looking embryos than the number that is appropriate to transfer into the uterus during the treatment cycle, then additional embryos can be frozen and stored in liquid nitrogen for future use. Once frozen, the embryos can be maintained in storage for many years, but, whenever possible, we encourage replacement within 2 years of fertilization.
Embryo cryopreservation is a well established and highly successful procedure. Therefore, most embryos are expected to survive freezing and thawing even though some embryos may lose one or more cells. However, a few embryos may not survive or be lost in the process of cryopreservation. Freezing is associated with slight reduction in the viability of most surviving embryos. Consequently, the chances of a live birth are somewhat lower with frozen-thawed embryos compared to fresh embryos. Most of this difference in live birth rates is due to the widespread practice of selecting the best embryos for fresh transfer. Therefore, a direct comparison between live birth rates after fresh and frozen transfers may be misleading because of this strong selection bias.
However, the health of babies born from frozen embryos is not affected by cryopreservation. Offspring born from frozen embryos have the same rate of congenital abnormalities as the general population. When damage occurs during the freezing process, the pregnancy usually does not ensue. The likelihood of achieving a live birth following transfer of frozen-thawed embryos in our program has been about 25-30% per transfer.
The consent form for embryo freezing requests that you indicate how you would like to dispose of the frozen embryo(s) in case of divorce and death. The options include donating the embryos anonymously for the benefit of another infertile patient, donating them for research or discarding them. While the embryos remain in storage, you need to pay an annual fee. The amount of the storage fee increases sharply for each additional year of storage.