HCS

HCS, or human chorionic somatomammotropin, is a peptide hormone produced by the placenta during pregnancy. Also known as placental lactogen (PL), hCS belongs to the growth hormone/prolactin family and is encoded by genes in the placental portion of the chromosome 17 cluster, primarily CSH1 and CSH2, which give rise to placental lactogen A and B forms. The hormone is secreted by the placental syncytiotrophoblast into maternal and fetal circulation.

Biochemically, hCS proteins are similar in structure to growth hormone and prolactin and are typically around 20–25 kilodaltons in size. They act via receptors related to the growth hormone and prolactin signaling pathways, leading to wide-ranging metabolic and developmental effects rather than a single target. hCS circulates at increasing levels as pregnancy progresses, peaking in the third trimester and declining rapidly after delivery.

Physiological role of hCS includes modulation of maternal metabolism to prioritize fetal glucose supply. It promotes lipolysis and can induce a state of maternal insulin resistance, helping to raise blood glucose availability for the fetus. It also influences pancreatic beta-cell growth and function, supporting increased insulin production during pregnancy. In addition, hCS contributes to mammary gland development in preparation for lactation, though its lactogenic role is less prominent than that of prolactin.

Clinical relevance of hCS centers on placental function and fetal growth. Abnormal hCS levels have been studied as potential markers of placental insufficiency or altered fetal growth, but measurement is not routinely used as a standalone diagnostic test. Variations in hCS expression can reflect placental mass and function, with broader implications for pregnancy outcomes.