Embryo loss (also known as embryo death or embryo resorption) is the death of an embryo at any stage of its development which in humans, is between the fifth and tenth week of gestation. Failed development of an embryo often results in the disintegration and assimilation of its tissue in the uterus. Loss during the early stages of prenatal development of the fetus results in the similar process of fetal resorption. Embryo loss often happens without an awareness of pregnancy, and an estimated 40 to 60% of all embryos do not survive.