betahCG

Beta-hCG, or the beta subunit of human chorionic gonadotropin, is a glycoprotein hormone produced mainly by placental trophoblasts after implantation. Human chorionic gonadotropin is a heterodimer consisting of an alpha subunit, shared with LH, FSH, and TSH, and a beta subunit that provides biological specificity. The beta subunit is the portion most often detected by pregnancy tests and is used in certain clinical assays.

Biological role and production: beta-hCG acts through the LH receptor to support the corpus luteum in early pregnancy, maintaining progesterone production until the placenta takes over. It participates in placental development and can influence maternal immune tolerance to the fetus. Outside pregnancy, elevated beta-hCG can occur in germ cell tumors and gestational trophoblastic disease; some assays specifically measure free beta-hCG for tumor marker purposes.

Production and kinetics: beta-hCG is secreted by placental trophoblasts shortly after implantation. Serum levels rise rapidly in the first trimester, typically doubling every 48–72 hours, and then decline to low but detectable levels as pregnancy progresses. In nonpregnant individuals, detectable beta-hCG prompts evaluation for pregnancy loss, ectopic pregnancy, or malignancy.

Measurement and clinical use: beta-hCG is measured in serum or urine. Pregnancy tests detect hCG, and quantitative serum beta-hCG is used to confirm pregnancy and monitor its progression, diagnose ectopic pregnancy or miscarriage, and assess viability. In oncology, beta-hCG testing supports diagnosis and monitoring of germ cell tumors and gestational trophoblastic disease.