Hyperemesis gravidarum is extremely severe nausea and excessive vomiting during pregnancy.
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.
The thyroid gland may become slightly and temporarily overactive (called hyperthyroidism).
Rarely, hyperemesis gravidarum continues after 16 to 18 weeks of pregnancy. If it does, it may severely damage the liver, causing jaundice and degeneration of liver tissue. If hyperemesis gravidarum severely damages the liver or causes severe dehydration, women can become confused.