Briefly, embryo freezing is a procedure that adapts to the developmental stage of the embryo. Embryos are placed in prepared media designed to protect embryos from extremely low temperatures. An instrument, controlled by a computer, slowly reduces the temperature of the solution until it reaches –80C Embryos are then labelled and stored individually in tanks filled with Liquid Nitrogen which maintains a temperature of –196C. No biological activity can be observed at these temperatures, and embryos can be stored until the patient is ready for them to be thawed. The freeze-thaw procedure yields a 20% loss of vitality, and those embryos that survive have a subsequent 1/3 chance of implantation compared with fresh embryos. Technology, however, is continually improving survival rates. Technically, frozen embryos can be stored indefinitely depending on the couple’s decision. Although conventionally, embryos are stored for a maximum of 3-5 years, case reports show that embryos can be stored for extended periods. By having couples renew their contract yearly, they can decide whether they want to thaw and transfer the embryos back to the uterus, destroy them or donate the embryos to research.
If there are excess good quality embryos after embryo transfer, these can be frozen and stored. Even though not all embryos will survive the freeze-thaw procedure, pregnancy rates have approached fresh embryo transfers. Embryo freezing has become an established method and has been practised for nearly 20 years, particularly in situations where many oocytes have been retrieved—freezing after embryo formation has provided a second chance for couples whose first attempt did not result in pregnancy. Preparation of the patient for a thawed embryo transfer is medically simpler and less intrusive. In some cases, patients come back to transfer the stored embryos to conceive a second child.
Embryos can be frozen at any point during their development. One can see fertilised eggs on the first day, and then the zygote begins dividing to become an embryo. On the 5th day, the embryo becomes a blastocyst, a stage that shows better results after the freeze/thaw procedure.
The Health Ministry in our country has extended the duration of embryo storage to 5 years. Electronic records where only authorised people with a password can access are made of each patient file. These records have five backups made daily and stored in different places. Two copies are stored in another building for safety in the event of the destruction of the whole building, such as fire, earthquake etc.
This is a method where embryos are frozen quickly to prevent ice crystal formation. When the solution freezes, it solidifies to form a glass-like appearance. This procedure aims to avoid ice crystal formation inside the cell while the temperature is reduced. DMSO (DimethylSulfoxide) and Ethylene Glycol are the most commonly used cryoprotectants. After the embryos are labelled, they are plunged directly into Liquid Nitrogen. Currently, vitrification has become more popularly used in most IVF clinics as the method has shown better survival rates and pregnancy rates than the slow freezing process.