Unborn young of any vertebrate, particularly mammals, after it has acquired its basic form. In humans, this stage begins about eight weeks after conception (see embryo). The fetal stage, marked by increased growth and full development of the organ systems, climaxes in birth (see pregnancy, parturition). By the end of the third month, the arms and legs of the human fetus begin to move and reflexive movements (such as sucking) begin. Four months after conception, the fetus is about 5.3 in. (135 mm) long and weighs about 6 oz (170 g). During the fifth month, downy hairs (lanugo) cover the body and the skin becomes less transparent. At seven months, a protective greasy substance (vernix caseosa) covers the reddish, wrinkled skin. Fat is deposited under the skin during the eighth month, when the fetus typically weighs about 5 lbs (2.2 kg). A full-term fetus is about 266 days old.
Learn more about fetus with a free trial on Britannica.com.
Who Can See Pictures of Tiny Foetuses Yawning and Jumping and Be CERTAIN Abortion Is Not Wrong? Steven Glover Argues, in This Deeply Personal Piece, That Men's Opinions Are Just as Valid as Women's in the Abortion Debate
Jun 29, 2004; Byline: STEPHEN GLOVER AS A MAN, do I have a right to a view on abortion? Many women would say no. They might not mind if I were...