Morning sickness is a term used to describe nausea and vomiting that occurs during pregnancy. It begins around the fourth week and often ends by the twelfth week. In some cases it may last until the end of pregnancy. It is a normal occurrence but in some cases it may be excessive and distressful. What are the causes? The exact cause of morning sickness is not known. It may be caused by hormonal changes or lower blood sugar levels that occur during early pregnancy. What is Hyperemesis Gravidarum? It is a term used to describe severe and persistent vomiting during pregnancy. It may be associated with weight loss, dehydration, electrolyte imbalance and psychological problems like depression, anxiety and isolation. If not treated, it may endanger the health of the mother and the foetus.