Fetus

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A fetus (pronounced /ˈfiːtəs/; also spelled foetus, fœtus, faetus or fætus, see below) is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.

In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.[1] [2]

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Etymology and spelling variations

The word fetus (plural fetuses) is from the Latin fetus, meaning offspring, bringing forth, hatching of young.[3] It has Indo-European roots related to sucking or suckling, from the Aryan prefix bheu-, meaning "To come into being".[4]

Fœtus or foetus is the British, Irish and Commonwealth spelling, which has been in use since at least 1594.[4] It arose as a hypercorrection based on an incorrect etymology (i.e. due to insufficient knowledge of Latin) that may have originated with an error by Saint Isidore of Seville, in AD 620.[5] This spelling is the most common in most Commonwealth nations (except in medical literature, where its use is barred). The etymologically correct original spelling, fetus is used in Canada and the United States. In addition, fetus is now the standard English spelling throughout the world in medical journals.[6] The spelling "faetus" was used historically.[7]

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