What does a pregnancy test detect?

A pregnancy test detects HCG, or human chorionic gonadotropin, which is a hormone produced by the placenta shortly after a fertilized egg attaches to the uterine lining. The presence of HCG in a woman's urine or blood indicates that she is pregnant. Most home pregnancy tests are designed to be sensitive enough to detect HCG levels even at very early stages of pregnancy, usually around the time of missed menstruation.

The other hormones mentioned—LH, FSH, and Estrogen—are involved in different physiological processes. LH, or luteinizing hormone, plays a key role in regulating the menstrual cycle and ovulation. FSH, or follicle-stimulating hormone, is critical for the development of ovarian follicles and sperm production. Estrogen primarily regulates the menstrual cycle and reproductive system, but none of these hormones serve as a direct indicator of pregnancy like HCG does. Therefore, the detection of HCG is specifically linked to confirming pregnancy, making it the correct answer.