Women with hyperemesis gravidarum, unlike women with ordinary morning sickness, lose weight and become dehydrated.
Doctors diagnosis hyperemesis gravidarum based on symptoms and do tests to check for dehydration and other possible causes of the vomiting.
Treatment involves nothing by mouth at first, fluids containing electrolytes and vitamins given by vein, and drugs to relieve the nausea.

(See also Nausea and Vomiting During Early Pregnancy.)
Pregnancy complications, such as hyperemesis gravidarum, are problems that occur only during pregnancy. They may affect the woman, the fetus, or both and may occur at different times during the pregnancy. However, most pregnancy complications can be effectively treated.
Pregnancy frequently causes nausea and vomiting. It usually occurs in the morning (as so-called morning sickness), although it can occur any time of day.
Hyperemesis gravidarum differs from ordinary morning sickness. If women vomit often and have nausea to such an extent that they lose weight and become dehydrated, they have hyperemesis gravidarum. If women vomit occasionally but gain weight and are not dehydrated, they do not have hyperemesis gravidarum.
The cause of hyperemesis gravidarum is unknown.