HCG stimulates the pituitary to produce the GnRH that is used by the hypothalamus to produce LH, FSH, and pregnenolone. Pregnenolone can be used by the body to produce whichever hormone that is still lacking. I have read somewhere one of the byproducts also created is TSH
Whenever the body has a hormone it needs, it converts part of another hormone into the one it needs. Because the body works in a negative loop situation, it only produces what it needs; if the hormone is available, the body wonāt produce it. If it is not available then the body converts existing hormones into it, or just produces when needed.