Are the sore breasts in earliest stages of pregnancy a result HCG hormone?

Yes, the sore breasts in the earliest stages of pregnancy are the result of the HCG hormone.

The human chorionic gonadotropin (HCG) hormone is produced by the placenta after implantation of a fertilized egg in the uterus. It is responsible for several changes in the woman's body during pregnancy, including the development of the corpus luteum, the increased production of progesterone, and the growth of the uterine lining.

HCG also stimulates the mammary glands to produce milk, which is why some women experience breast tenderness or soreness in the early stages of pregnancy. This soreness is usually mild and goes away after a few weeks.