Thus implantation signals the beginning of the embryo stage and the preg nancy begins. During these early divisions no differentiation of cells has occurred. Each of these cells has the potential to become a separate individual if the cell becomes separated from the zygotic cell mass. Scientifically, pregnancy begins when the hormone HCG is produced by the uterine lining upon implantation of the zygote. Currently 2 million American couples per year seek treatment for infertility at 20 U.S. in vitro fertilization clinics.
Infertility affects men and women about equality.