Embryo Freezing
Introduction
Embryo freezing or cryopreservation is a technique which has added an important dimension to assisted reproduction.
This procedure has various advantages like:
1. Embryo freezing gives an additional opportunity to couples when fresh cycles of assisted reproduction fail. Embryos can be also stored for future use after one successful embryo transfer.
2. Social and ethical issues of disposing the embryos are eliminated.
3. It also eliminates the risk of implantation of too many embryos which also avoids multiple gestations(triplets or quadruplets)
4. Embryo wastage is avoided by freezing.
5. Embryo freezing increases chances of pregnancies per IVF cycle by 10 to 30%.
6. There is no increase in birth defects, congenital or developmental anomalies with this method.
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We define embryos survival depends on percentage of cells viable after thawing.
1. Survived- if >50% of the cells are viable.
2. Partially survived if <50% of its cells are viable.
3. Atretic if the entire thaw is dead.
Candidates for cryopreservation:
1. Couples who are undergoing IVF currently. These couples can store embryos for next time when they need to conceive again. This obviates the need of again going through hormone injections, surgical procedures, doctor’s visits, and the emotional and financial burden.
2. Couples in which one of the partners has cancer can freeze their embryos before undergoing chemotherapy or radiotherapy. As these treatments can abolish the ability to produce healthy eggs or sperm. They can use these embryos after recovery.
3. Infertile couples or single women who can use frozen donor embryos to become pregnant.
4. Women in which embryo implantation is compromised because of diseases like endometrial polyposis, poor endometrial development, or dysfunctional uterine bleeding near the time of embryo transfer.
5. Diseases causing difficulty at the time of fresh embryo transfer, e.g. cervical stenosis (inability to pass through the cervical canal because the cervix is narrowed or scarred).
Process for embryo freezing:
1. Embryos can be frozen during any time from one to five days after fertilization after good quality is assured.
2. Depending on the number of embryos that are probable to be transferred into the woman’s uterus, they are stored in the batches of one or more.
3. Embryos are mixed with a cryoprotectant solution during the freezing process to protect them. This solution helps in preventing formation of ice crystals in the cells which can destroy embryos.
4. Embryos are then stored in liquid nitrogen freezers at a very low temperature in glass vials. They are cooled slowly to -196° C (-400°F) using a specialized machine.
5. To use again for IVF, these embryos are thawed again and immersed in solutions to remove cryoprotectant from the thaw.
What are the success rates of the procedure?
Embryos can be frozen deeply for almost 10 years and still remain viable. But many times, they do not survive the freezing and thawing process. The embryos surviving are often not as healthy as fresh embryos. The rate of pregnancy with frozen embryos is lower than that of fresh embryos.
Disadvantages of Embryo Freezing:
This is a very scientific procedure but some points are worth mentioning:
1. Very little data is available regarding the long term effects of this procedure of freezing as it is a much specialized method.
2. The process of cryopreservation is delicate and complex. The fragile embryos may not survive the entire process.
3. There is another highly controversial issue of ethical, religious and moral concerns about the procedure. Some couples prefer egg or sperm preservation over this procedure because of moral concerns.
4. Cryopreservation is very expensive procedure and is conducted in only few specialized fertility centres. The cost also must be weighed over advantages.
To conclude, cryopreservation offers couples a very convenient and specialized option of assisted reproduction when exploring treatment options for fertility. It also allows new couples more flexibility with regards to family planning. Couples can prolong the biological clock of fertility by utilizing freezing technique.