Morning sickness is a term used to describe the nausea or vomiting many women experience during pregnancy. Other signs and symptoms including weight loss, lightheadedness and fainting may accompany morning sickness. Researchers have been unable to identify the exact cause of morning sickness, but many experts believe the condition may be caused by changes in hormone levels.

Although its name suggests that it only occurs in the morning, morning sickness can occur at any time of day. There are a number of factors that can trigger the nausea or vomiting associated with the condition. It is most common during the first trimester (first three months of pregnancy) and usually disappears by the fourth month of pregnancy. For some women, however, it may continue for the entire pregnancy. Other women never experience any morning sickness during their pregnancy.

Although the nausea and vomiting associated with the condition may be unpleasant for most expectant mothers, it usually does not result in harm for the woman or her fetus. Hyperemesis gravidarum (a disorder characterized by frequent and severe vomiting), however, can lead to dehydration and may require hospitalization.

When nausea and vomiting are severe, an obstetrician-gynecologist (ObGyn) may perform a physical examination and order blood tests (e.g., complete blood count, chem-20) and urine tests. These tests can help detect dehydration and determine if the symptoms are related to a condition other than morning sickness.

According to the National Institutes of Health (NIH), most pregnant women experience some degree of nausea and about one-third have vomiting. Mild to moderate morning sickness may be successfully treated with changes in behavior and nutrition. For example, a woman may benefit from eating five or six small meals a day rather than three large meals. Avoidance of certain foods also may reduce morning sickness in women. Although rare in most pregnant women, severe nausea and vomiting may require treatment, including medication or intravenous fluid administration.