When are embryos frozen?
Excess embryos retrieved from an IVF, ICSI or IMSI are usually frozen for later cycles.
How are embryos frozen?
Rapid cooling protocol (vitrification) involves media containing higher concentration of cryoprotectants and has a relatively much shorter freezing time.The main concern when freezing embryos is the formation of ice between the cells.This can be easily avoided by a highly skilled embryologist.
Slow cooling involves seeding where the cryopreservation straw is manually touched by a cold forceps dipped in liquid nitrogen further away from the embryo to initiate ice formation which gradually spreads to the rest of the solution containing the embryos. This prevents the damage to the embryos.
Most centers today apply vitrification for freezing embryos.
During this procedure the frozen sperm/oocytes/embryos are thawed (de-frozen) to room temperature, observed for further development and then transferred into the patient’s uterus after stimulating endometrial growth. At the time of embryo replacement, the straws are removed from the liquid nitrogen and placed in a water bath at room temperature before re-hydrating with special media. At the end of re-hydration, the embryos are cultured in media within the carbon dioxide incubators and allowed to develop further either to day 2 or blastocyst prior to transfer.
How safe is embryo freezing?
There are over 300,000 children born worldwide from frozen embryos without an increase in birth defects.It is scientifically proven that embryos can be indefinitely stored, thawed and later transferred.