Final answer:
Human chorionic gonadotropin (hCG) is the hormone secreted by the pituitary during fetal development in young children and pregnant women, and is notably increased during the early stages of pregnancy.
Step-by-step explanation:
The hormone that is secreted by the pituitary during fetal development in very young children and in pregnant women, but isn't usually found in adults, is Human chorionic gonadotropin (hCG). While the anterior pituitary produces several hormones, including growth hormone (GH), prolactin, and thyroid-stimulating hormone (TSH), it is hCG that is notably increased during pregnancy. hCG is produced by the placenta and indicates the presence of a developing embryo. The levels of hCG typically peak during the first trimester and are the basis for standard pregnancy tests.