A client presents to the clinic reporting a missed period and a positive home pregnancy test. The nurse explains the mechanism of pregnancy tests detect the presence of _________ in urine or blood.

Pregnancy tests work by detecting the hormone human chorionic gonadotropin (hCG), which is produced by trophoblastic cells of the developing placenta shortly after implantation. hCG maintains the corpus luteum, allowing continued secretion of progesterone to support the early pregnancy. Its levels rise rapidly in the first trimester, making it a reliable indicator of pregnancy in both urine and blood samples.