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).

• Symptoms of pregnancy
• Severe nausea
• Persistent excessive vomiting (often leading to weight loss)
• Lightheadedness or fainting

Signs of dehydration may occur, including:

• Ketones in urine
• Increased hematocrit
• Increased pulse rate
• Decreased blood pressure

Blood tests may be recommended for further evidence of dehydration.

Uncomplicated nausea may be treated with dry foods such as crackers and small, frequent meals. Emotional support may also help with nausea and/or vomiting.

It is important for a pregnant woman to maintain her fluid intake. Fluids should be emphasized during the times of the day when she feels least nauseated. Seltzer or other sparkling waters may be helpful.

Medication to prevent nausea is reserved for cases where vomiting is persistent and severe enough to present potential maternal and fetal risks. The most severe cases may require hospitalization with IV fluid administration.

An evaluation to rule out abnormalities of the liver or gastrointestinal tract may be necessary in cases of persistent symptoms.

Psychosocial support is an important part of treatment -- most nausea and vomiting during pregnancy is normal, although unpleasant.

Nausea and vomiting usually peaks between 2 and 12 weeks gestation and resolves by the second half of a pregnancy. With adequate identification of symptoms and careful follow-up, this sickness rarely presents serious complications for the infant or mother.

Social or psychological problems may be associated with this disorder of pregnancy. If such problems exist, they need to be identified and addressed appropriately.

Call your health care provider if you are pregnant and are experiencing severe nausea with vomiting.