Which hormone is present as early as 10 days after conception?

Human chorionic gonadotropin (hCG) is the hormone that is present as early as 10 days after conception. This hormone is produced by the developing placenta shortly after the embryo attaches to the uterine lining. It plays a critical role in early pregnancy by maintaining the corpus luteum, which in turn helps to produce progesterone, essential for sustaining the pregnancy in its initial stages.

Detecting hCG is the basis for many pregnancy tests, as it can be identified in a woman's blood or urine shortly after implantation. Its presence signifies that the body is initiating preparations for the continued development of the fetus. In contrast, other hormones listed, such as luteinizing hormone, progesterone, and prolactin, do not have the same early presence or specific function in terms of early pregnancy detection.