Growth of human preimplantation embryos in vitro.

The human oocyte fertilizes and develops into embryos in the Fallopian tube and reaches the uterus only after compaction. However, for several years embryos that were developed following in-vitro fertilization (IVF) were transferred into the uterus on day 2 or 3 at the 4-8 cell stage in contrast to the in-vivo situation where they would be present in the Fallopian tube. Earlier attempts to grow embryos in vitro for 5 to 6 days were not always successful. Attempts were therefore made to understand the in-vivo environment of the Fallopian tube where the early embryonic development occurs. This article reviews the studies carried out to understand the composition of fluids in the Fallopian tube specifically with reference to the energy metabolites - lactate, pyruvate and glucose; it also covers how the formulation of culture media for human IVF and embryonic development were modified over the years based on some classical work done on embryo culture in laboratory animals.