Human chorionic gonadotropin (hCG) is known as the pregnancy hormone because its levels increase once a pregnancy is established. hCG is also used to initiate ovulation in assisted reproductive technology cycles where GnRH agonists or antagonists are used.

Once a pregnancy is established, the placenta begins to produce hCG, which helps maintain the pregnancy. A spike in hCG levels initiates ovulation. Pregnancy outcomes can be determined by the rate that hCG rises over the course of the pregnancy.

hCG/Pregnyl/ or ovidrel are administered 24-26 hours prior to an intrauterine insemination (IUI) or 36 hours prior to egg retrieval during an IVF treatment cycle.