# Human Chorionic Gonadotropin --- **Human chorionic gonadotropin** or **hCG** is a hormone released by the trophoblast cells of the [[placenta]] that signals to the [[corpus luteum]] to continue secreting [[estrogen]] and [[progesterone]]. hCG signals the corpus luteum that fertilization and implantation have occurred, which makes it so the corpus luteum does not go away after the luteal phase. Instead it stays around for the next 3 months, producing both progesterone and estrogen until the placenta is developed enough to produce those as well. This makes it so the uterine lining keeps thickening and doesn't slough off. ![[pregnancy hormones.png]] ## Pregnancy Tests **Pregnancy tests**, like the kind that you can buy at any pharmacy detect the presence of hCG in the urine. The placenta starts to release hCG fairly early, and it's only ever produced after a successful fertilization, so it's a good marker. Newer tests can detect pregnancy as soon as 7-9 days after ovulation. The first void of the morning is the most accurate, but any urine will test positive if there's enough hCG. hCG grows exponentially as the pregnancy continues, so if the test is negative and the patient is expecting a positive, they can retest in 4-7 days. A urine pregnancy tests is a qualitative sign of pregnancy. A *serum* hCG is a *quantitative* test, as it can read the *amount* of hCG a patient has in their bloodstream. ___