Embryofrysning

Embryofrysning, or cryopreservation of embryos, is a medical procedure used in assisted reproductive technology to preserve embryos created during in vitro fertilization (IVF) or other ART procedures for later use. Freezing embryos allows subsequent pregnancy attempts without repeating ovarian stimulation and egg retrieval.

During the process, after ovarian stimulation and fertilization, surplus viable embryos may be selected for freezing. The two main methods are slow freezing and vitrification. Vitrification, a rapid cooling technique, is the standard today due to higher survival rates after thawing. Embryos are treated with cryoprotectants and stored in liquid nitrogen at about -196°C in specialized storage facilities, kept in labeled containers with records of their developmental stage.

Frozen embryo transfer (FET) cycles use thawed embryos to establish pregnancy. Freezing offers flexibility, helps maximize the use of produced embryos, and can improve cumulative pregnancy rates. Success depends on embryo quality, the age of the woman at the time of embryo creation, and the number of embryos transferred. Survival after thawing is high with vitrification, and pregnancy outcomes per transfer can be similar to or slightly lower than fresh transfers, depending on individual factors.

Safety and considerations: Most studies report no significant increase in congenital anomalies with frozen transfers compared with fresh transfers. Risks are those common to IVF, including potential pregnancy with multiple embryos and the need for reliable long-term storage. Ethical and legal aspects vary by country, including consent, disposition of embryos, and use of donor material.

Storage and limits: Embryos may be stored for many years; there is no fixed biological expiry, but storage duration is influenced by regulatory and policy frameworks in different jurisdictions. Advances continue to improve thaw survival and clinical outcomes.