Morning sickness is nausea that occurs during pregnancy. Morning sickness affects a large proportion of pregnant women. It is most common during the first trimester. Morning sickness does not hurt the baby in any way unless you lose weight, such as with severe vomiting. Mild weight loss during the first trimester is not uncommon when women have moderate symptoms, and is not harmful to the baby. The amount of morning sickness during one pregnancy does not predict how you will feel in future pregnancies.
Hormonal changes of pregnancy are thought to play a role. Rarely, severe or persistent nausea or vomiting may be caused by a medical condition unrelated to pregnancy such as thyroid or liver disease. Treatment isn't necessary for most cases of morning sickness. If your morning sickness symptoms persist, however, your pregnancy care provider may prescribe vitamin B-6 supplements, antihistamines and possibly anti-nausea medications. Other studies have found that you are 50 percent more likely to have morning sickness with severe nausea and vomiting if one is pregnant with a girl.