Essential facts Eight out of ten pregnant women are affected by nausea and vomiting in pregnancy. It is one of the most common reasons for pregnant women being admitted to hospital. Despite being known as morning sickness, symptoms can occur at any time of the day or night. The severe form of nausea and vomiting in pregnancy, hyperemesis gravidarum, is much rarer and affects up to 3% of pregnant women. For most women, their symptoms improve or disappear by around week 14, although for some it can last longer.