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Cryopreservation of Sperm, Embryos & Oocytes: The living tissues maintain their vitality and functions when stored below the freezing temperatures. The sperms, ova and embryos are stored to be used later. These are thawed and revived at the time of requirement.
Freezing of embryos and sperm is possible for either short or long term storage. Sperm have been successfully frozen for many years. Embryos can be successfully frozen and thawed 80-90% of the time. A similar procedure for immature eggs has recently been developed and is currently available.
Excess embryos are frozen and can be transferred at a later date. Sperm can be stored ahead of time and use during treatment cycles. Ovarian cryopreservation can be used to store large numbers of immature eggs for future use.
Cryopreservation of embryos is now routinely done at all the well equipped IVF centers. Excess embryos are cryopreserved for later use. About two thirds of embryos will survive the process of freezing and thawing. During an IVF cycle, all the available oocytes are subjected to fertilization. When the number of embryos exceeds the optimum number for transfer, the extras can be preserved. Usually 2 - 4 embryos are transferred to the uterus to maximize the chance of conception. If pregnancy does not occur during the stimulated cycle, the frozen embryos may be thawed and transferred to the uterus during a spontaneous menstrual cycle. If conception results from the initial cycle, cryopreserved embryos can be used later in an attempt to achieve another pregnancy. Advantage of Frozen embryo Transfer (FET):
- Transfer of the thawed embryo occurs in natural Ovarian cycle. Repeat ovulation induction is avoided.
- Women can have second baby without COH, oocyte retrieval & waiting for fertilization.
- Frozen embryos have been used by widows after death of their husbands with successful pregnancies.
- Added benefit is the lower cost since COH, egg retrieval, and fertilization procedures are not repeated.
Placement of Cryopreserved Embryos Natural Cycles. Embryo is thawed 1 day after ovulation, 2 days after LH peak and transferred the same day. Blastocyst is thawed 4 days after LH peak and transferred the same day (Day-6 blastocyst).
Programmed Cycle. Short acting GnRH agonist 0.2 mg is given from day 21 of previous cycle, 0.1 mg daily from day-1 of the menstruation until day 15. Estradiol is given from day 1 to 7 weeks and Progesterone from day 15 to 12 weeks of gestation.
Cryopreservation of Ova In the majority of IVF cycles, ovarian stimulation results in the production of several follicles and retrieval of multiple Oocytes. After 5-6 ova are subjected to fertilization, the rest can be preserved. These can be used subsequently and the woman is saved from ovarian stimulation and retrieval procedures. Theoretically attractive, IVF from thawed eggs is not very successful so rarely applied
Cryopreservation of Sperm have been done for many years. Sperms can be frozen and preserved. Frozen sperms are thawed to be available for IVF or artificial Insemination at appropriate time. It obviates the need of semen collection at fixed time, which some men find difficult. Sperms are frozen and preserved much before the procedure. It also helps where husband can’t be available at the appropriate time. This is also common in veterinary sciences to breed animals
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