Embryo transfer

Embryo transfer is the placement of an embryo into a recipient’s reproductive tract for gestation. In human assisted reproduction, it usually means placing an embryo in the uterus after in vitro fertilization.

In vitro fertilization: A method of fertilization in which eggs and sperm are combined outside the body, with resulting embryos transferred to a uterus. It produces the embryos used in most human fertility-treatment transfers.
Fresh embryo transfer: An embryo transfer performed during the same treatment cycle in which the eggs were retrieved and fertilized. It contrasts with delaying transfer to a later cycle.
Cleavage-stage embryo transfer: Transfer of an embryo at an early cell-division stage, commonly on day two or three after fertilization. It offers an earlier transfer point than blastocyst-stage transfer.
Implantation rate: The proportion of transferred embryos that implant, measured using a defined population and time point. It is one measure used to assess outcomes after embryo transfer.
Embryo transfer in livestock: The use of embryo transfer to reproduce or multiply desirable genetic lines in farm animals. Livestock breeding was an early and extensive setting for developing transfer techniques.
Embryo culture: The laboratory maintenance of embryos under controlled conditions before transfer or cryopreservation. Culture determines how long embryos develop before transfer and which are available.
Frozen embryo transfer: The placement of an embryo that was cryopreserved after fertilization and later thawed. It allows transfer in a cycle separate from egg retrieval and embryo creation.
Blastocyst transfer: Transfer of an embryo after development to the blastocyst stage, usually around day five or six. It extends laboratory culture and can help distinguish embryos by continued development.
Clinical pregnancy: A pregnancy confirmed by ultrasound visualization of a gestational sac or other specified clinical evidence. It distinguishes confirmed pregnancies from positive tests after transfer.
Walter Heape: A British reproductive biologist who reported successful embryo transplantation between rabbits in 1890. His rabbit experiments are an early landmark in mammalian embryo transfer.

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