fetus /fē″təs/ [L, fruitful] , the unborn offspring of any viviparous animal after it has attained the particular form of the species; more specifically the human being in utero after the embryonic period and the beginning of the development of the major structural features, from the ninth week after fertilization until birth. Kinds of fetal anomalies include anideus, lithopedion, mummified fetus, parasitic fetus, and sirenomelia. Also spelled foetus. Compare embryo. See also prenatal development. −fetal, foetal, adj.
