Sperms, eggs and embryos are cryopreserved (frozen) from body temperature down to -196°C (-320° F) and stored in containers of liquid nitrogen called dewars. The gametes / embryos are kept within special labelled plastic vials, or straws, that are sealed prior to freezing.
Embryos may be frozen if they cannot be transferred during your IVF cycle. In certain cases, you might have more embryos than what you might need for a transfer. These surplus embryos can be stored for future use.
Egg freezing is done for women in certain scenarios. Some women wish to have children, but they have not found the right partner, or need more time to establish their career, or want to accomplish other life goals or are facing a medical problem or procedure that could impact their fertility. Egg freezing gives them an opportunity to preserve their fertility till the time that they are ready.
Semen freezing can be done if a man is unavailable when the woman is having fertility treatment. This is also a useful option if the man finds it difficult to provide a semen sample on demand.
Both eggs and sperms can be frozen if a person is planning to have cancer treatment. Chemotherapy and / or radiation can affect the ovaries and testes and prevent post treatment individuals from having children. Freezing, if done prior to such treatment thus helps in achieving a pregnancy when you are free of cancer. You can use your frozen eggs, sperms or embryos, which will be thawed and used at an appropriate time.
Freezing is generally done for a period of one year and then renewed according to the need of the patient.