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. Some women have nausea and vomiting through their entire pregnancy. Hormonal changes of pregnancy are thought to play a role. Changes include rapidly increasing oestrogen levels, an enhanced sense of smell, excess stomach acids, and increased fatigue. Some researchers think that stress and emotions also play a part in morning sickness.
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. Hyperemesis gravidarum tends to occur in the first trimester of pregnancy and lasts significantly longer than morning sickness.