Any of a range of techniques for improving the fertility of animals, including humans, in which eggs and/or sperm are extracted from the respective animal(s) for manipulation in some way. One of the best known is in vitro fertilization, in which ova (egg cells) are placed with sperm in a culture medium so that fertilization occurs and embryos start to develop. Healthy embryos are then selected and implanted in the mother’s uterus to continue their development. Such techniques are widely used to overcome certain forms of human infertility and in breeding elite livestock. Early-stage embryos can undergo genetic analysis, for instance to screen for certain genetic diseases or (in livestock) to select progeny with desirable genetic traits or a particular sex.