All of the following stages must occur for a woman to get pregnant. however, after which stage can a woman be described as pregnant?

Pregnancy is declared from the appearance of beta HCG hormone in the woman's urine or blood. 
The hormone HCG (Gonadotropic Chorionic Hormone) is secreted by the placenta from the implantation of the embryo into the uterus. If there has been fertilization, the HCG rate exceeds 8 IU at implantation and then starts to double every other day.
So we can conclude that pregnancy is described at the stage of implantation.

Processes above and be sure to mention the movement of electrons and energy as the carbon atom moves from one reaction to another.