Hyperemesis gravidarum

Hyperemesis gravidarum is extreme, persistent nausea and vomiting during pregnancy that may lead to dehydration.

Nearly all women experience some degree of "morning sickness" -- nausea and vomiting during pregnancy, particularly during the first trimester. The cause of nausea and vomiting during pregnancy is believed to be rapidly rising serum levels of a hormone called HCG (human chorionic gonadotropin) secreted by the fetus. Increased estrogen levels have also been implicated.

Researchers theorize that during human evolution, sickness during pregnancy protected the fetus by making the mother too nauseous to eat foods that were most likely to be toxic to the early pregnancy. Support for this idea comes from the fact that many of the foods that tend to repulse pregnant women contain potentially harmful substances. Also, women who have virtually no nausea or vomiting appear to be more likely to miscarry than those who experience some sickness.

However, too much vomiting can interfere with the weight gain needed to sustain the pregnancy and cause dehydration, which can be harmful to both mother and child. Extreme nausea and vomiting during pregnancy may indicate multiple pregnancy (twins or more) or, extremely rarely, hydatidiform mole (abnormal tissue growth that results from conception but does not give rise to a viable fetus) or thyroid disorder.

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