The hormone that prevents pregnancy is progesterone.
According to the provided reference, "[Progesterone is the hormone that prevents pregnancy]([1] Birth control pills are primarily used to avoid pregnancy. The type of medicine used estimates the effectiveness of these oral contraceptive medicines.), and the estrogen component controls menstrual bleeding."
In the context of birth control pills, which are primarily used to avoid pregnancy, progesterone plays a crucial role in preventing ovulation and therefore, pregnancy.
