It is not known exactly what causes hyperemesis gravidarum. Doctors suspect that it may be related to levels of the hormone HCG (human chorionic gonadotropin), a pregnancy hormone released by the placenta. In some cases, extreme nausea and vomiting accompanies pregnancies with multiple fetuses, and can also be caused by hydatidiform mole (molar pregnancy).
Risk factors such as a prior pregnancy involving hyperemesis gravidarum and a family history of the condition create a greater likelihood of it affecting a pregnancy.
While the causes of hyperemesis gravidarum may not be known, it can be effectively treated.