Cryopreservation or freezing is a technique, in which the body cells/ tissue are frozen in ice for use at a later date. The frozen specimen is recovered intact when its time to use the by a process called thawing. This technique is now used quite commonly in fertility management and can be used to freeze eggs, sperms or embryos depending on the requirement. Freezing technology has evolved over time and the pregnancy rates using frozen sperms/ eggs/ embryos are as good as with fresh ones.
The technique of cryopreservation has evolved over time, with vitrification being a major breakthrough in this field. The term vitrification is derived from a Latin word “vitrium”, which means “glass”. The process of vitrification involves cooling the embryos rapidly, which turns the cellular content into a glass like substance without allowing any time for formation of ice crystals. Ice formation risks the cell rupture because water expands when it forms ice. The embryos are than dipped in liquid nitrogen and stored in at ¬–196 degree centigrade. This brings all cellular activity to a halt and allows the embryos to remain viable for indefinite period of time. The recovery rate on thawing the vitrified embryos is excellent. Therefore, embryo cryopreservation has now become an excellent tool for freezing the embryos. Embryos can be frozen at any stage of development from day 1 to day 5. We prefer to allow the embryos to grow for some time before freezing, so that the quality of embryos formed using IVF/ ICSI can be assessed and we freeze only the good quality embryos with high potential of producing pregnancy on being transferred.
1. Extra good quality embryos formed after IVF/ ICSI- These frozen embryos can be used later in case the initial transfer fails or the couple decides to try for another child after a first successful embryo transfer.
2. Embryo freezing allows for transfer of lesser (more justified) number of embryos, thus reducing the risks of multiple pregnancies.
3. Embryo freezing reduces the complications rates in patients who are hyper stimulating, as embryo transfer can be deferred to a later (cold) cycle. This happens as the physiological status of the hyper stimulating woman is more settled in a later cold cycle.
4. Embryo freezing offers an option to couples desirous to having a child later, but are at risk of losing their fertility because of some surgery or gonadotoxic treatment like radiotherapy of chemotherapy.
Eggs can be frozen using the same technique of “vitrification”, as described above for embryo freezing. The most common indications for cryopreservation of eggs include:
1. Women with advanced age, but still waiting for a right partner, can get their eggs cryopreserved for use in future.
2. For fertility preservation in fertile women undergoing any treatment that can suppress or reduce their fertility after the treatment- such as chemotherapy, pelvic radiation, surgery.
3. Sometimes eggs retrieved from donors can be cryopreserved to build an oocyte bank.
Sperm freezing is a rather simpler and well defined procedure and has been in use for decades. Sperms stand the freezing process very well and can be thawed easily.The common indications for sperm freezing include:
1. As a backup in cases where the male partner may not be available on the day of IUI/ IVF to provide fresh semen sample
2. When there is apprehension of the male partner not being able to produce a semen sample on the day it is needed.
3. Before the male partner is to undergo treatments like chemotherapy, which will likely affect his sperm count adversely and even make him azoospermic.
4. In men with oligospermia where multiple semen samples may be frozen to accumulate sperms.
5. In azoospermic males where the sperms have been recovered surgically using techniques like MESA, PESA, TESA. Sperms can be frozen in multiple aliquot to help the patient avoid having to have the surgery again.