foetus

A foetus is the term used in human development to describe the unborn offspring after the embryonic period and before birth. In humans, a foetus generally denotes the developing child from the end of the eighth week of gestation (about two months after conception) until delivery. The earlier phase, when organ systems are forming, is called the embryonic period; cells differentiate to form tissues and organs during that time.

During the foetal period, growth proceeds mainly by enlargement and maturation of already formed organs. The foetus is sustained in the uterus by the placenta, which transfers oxygen and nutrients from the mother's blood, and by the umbilical cord and amniotic fluid, which cushion and support development. Fetal movements and reflexes begin earlier but become more noticeable later in pregnancy.

By the second trimester, many organs are functioning in a basic way, and by the third trimester the lungs and other systems mature in preparation for breathing after birth. Term pregnancy is typically around 37 to 42 weeks of gestation; most births occur around 38 to 41 weeks.

Birth weight and length vary widely; a typical full-term baby weighs about 2.5 to 4 kilograms and measures around 50 centimeters at birth, though there is broad variation.

Medical care for foetuses includes prenatal screening and imaging, such as ultrasound, to monitor growth and identify congenital anomalies. Ethical and legal frameworks govern pregnancy, fetal rights, and medical decision-making in different jurisdictions.