Gamete Freezing: Options to Store Eggs, Sperm and Embryos
Cryopreservation of Embryos
Embryos that have not been selected for transfer back to the uterus during an IVF cycle are allowed to continue to grow to Day 6 with the hope of the option to freeze. Those embryos that are continuing to divide and meet specific criteria for potential viability on Day 5 or 6 are frozen (cyropreserved) at that time. Cryopreservation of the excess embryos provides an opportunity for achieving pregnancy at another time in the future, thus increasing the number of potential transfers from a single retrieval cycle.
The cryopreservation of oocytes or eggs is a relatively new technique in reproductive medicine. Cryopreservation of oocytes is more difficult than cryopreservation of embryos. The oocytes are more fragile because of their stage of meiosis (development). The structures within the oocyte, such as the spindle and the centromeres, are very delicate and, therefore, more susceptible to injury during the freezing process.
Because of the delicate nature of the chromosomes in eggs, the cryopreservation of eggs is less successful than the cryopreservation of embryos. For that reason, this procedure is primarily offered to patients undergoing treatment for cancer. It is also offered to some patients who do not have a partner and desire to delay their fertility. Due to recent advances in the promising new technique of vitrification, we anticipate that oocytes will soon be cyropreservedusing this method. We expect that this will produce an increase in the chance for survival and pregnancy.
Sperm may be cyropreserved for patients who will be undergoing an IVF procedure at Austin IVF or who will have an IUI procedure at Texas Fertility Center. The reasons for freezing sperm vary, but usually include one or more of the following situations:
- before chemotherapy or radiation treatment for cancer
- as a back-up sample in case of anticipated difficulty with the collection of a semen sample needed for IVF or IUI
- as a back-up when a semen sample contains a very low number of motile sperm
- when work schedules and travel may interfere with the collection of a semen sample on the day of a planned procedure