Morning sickness is nausea and vomiting that occurs during pregnancy. And, despite its name, morning sickness can strike at any time of the day or night. Many pregnant women have morning sickness, especially during the first trimester. But some women have morning sickness throughout pregnancy. Rarely, morning sickness is so severe that it progresses to a condition called hyperemesis gravidarum. This is when someone with nausea and vomiting of pregnancy has severe symptoms tha