The hormone found only in pregnant women that, when detected, confirms pregnancy is

Human chorionic gonadotropin hormone (hCG)

This hormone is produced by a woman only during pregnancy and is responsible for "pregnancy symptoms," such as vomiting and nausea.

It is primarily produced by the placenta shortly after the dividing fertilized egg cell (embryo) attaches or implants itself into the uterine lining (endometrium). This occurs a few days after the woman has conceived.