What does a pregnancy test detect?

A pregnancy test detects human chorionic gonadotropin (hCG), which is a hormone produced by the placenta shortly after a fertilized egg attaches to the uterine lining. The presence of hCG in urine or blood is a reliable indicator of pregnancy. This hormone typically begins to be produced around six days after fertilization and levels continue to rise rapidly in the early stages of pregnancy, making it a key marker for testing.

The other hormones listed have different roles in the reproductive system. Luteinizing hormone (LH) is primarily involved in triggering ovulation and is used in ovulation tests rather than pregnancy testing. Follicle-stimulating hormone (FSH) plays a vital role in the maturation of ovarian follicles and is often measured in fertility assessments rather than in pregnancy tests. Estrogen, while important in maintaining pregnancy and regulating menstrual cycles, is not used as a marker for pregnancy in standard tests. Thus, hCG is the specific substance that pregnancy tests are designed to detect, confirming the presence of pregnancy.