hCG (Human Chorionic Gonadotropin)

hCG is structurally similar to LH and binds the same receptor. In fertility treatment, an injection of hCG (e.g., Novarel, Pregnyl, or recombinant choriogonadotropin alfa/Ovidrel) is given 34–36 hours before egg retrieval to trigger final egg maturation and simulate the natural LH surge.

For monitoring early pregnancy, the beta subunit of hCG (beta hCG) is measured in blood. hCG levels double roughly every 48–72 hours in a healthy intrauterine pregnancy. Very high hCG levels (such as from exogenous trigger shot) can temporarily cause false-positive home pregnancy tests, which is why clinics ask patients to wait for the scheduled blood test rather than testing at home early.