Which hormone is tested to determine whether a person is pregnant?

The hormone tested to determine pregnancy is human chorionic gonadotropin, commonly referred to as HCG. When a woman becomes pregnant, the developing placenta produces HCG shortly after fertilization, which is essential for maintaining the early stages of pregnancy. HCG can be detected in urine or blood, and its presence is a key indicator of pregnancy.

Tests for HCG are widely used because they are both reliable and straightforward, making it the standard method for pregnancy testing. The hormone's levels can be quantitatively measured to assess not only pregnancy but also the health of the pregnancy over time, as HCG levels typically rise in early pregnancy.

In contrast, cortisol is a hormone related to stress response, estradiol is one of the main estrogens involved in the menstrual cycle and reproductive system, and free T4 is a thyroid hormone important for metabolism regulation. None of these hormones directly indicate pregnancy status, unlike HCG.