Morning sickness (also known as nausea and vomiting of pregnancy, NVP) is a misnomer as it is a condition associated with pregnancy which can occur at any time during the day. The symptoms typically appear between the fourth and sixteenth week of pregnancy, although about ten percent of women still have symptoms after the twentieth week.

The cause of morning sickness is unknown but may be related to changing levels of the hormones human chorionic gonadotrophin or estrogen. It could also be linked to an enhanced sense of smell, a sensitive stomach or pregnancy-related stress.

Morning sickness affects about 70-80 percent of all pregnant women to some extent and the symptoms are nausea and vomiting. It can negatively affect someone's quality of life, decrease the ability to work while pregnant, and result in healthcare expenses. Generally, mild to moderate cases have no effect on the baby and even severe forms usually have normal outcomes, with serious complications being very rare.

Taking prenatal vitamins before pregnancy may decrease the risk of morning sickness and specific treatment, other than a bland diet, may not be required for mild cases. If medical treatment is required, a combination of doxylamine and pyridoxine, which acts as an anti-nausea and anti-vomiting agent, is recommended initially and there is some evidence that ginger may be useful. In severe cases, if these methods have not helped, the antihistamine methylprednisolone may be tried. If women are experiencing such severe symptoms that they are losing weight, tube feeding may be required.