Morning sickness is nausea and vomiting associated with pregnancy. It is common in up to 70% of pregnant women during the 4th and 16th week of pregnancy, with about 10% of women continuing to suffer symptoms past the 20th week. Despite the use of "morning", the symptoms can, in fact, appear at any time of the day. In severe cases, women can actually suffer weight loss during pregnancy. It can be distinguished from other conditions by the absence of abdominal pain, fever or headache.
The underlying cause of the symptoms are still unknown. At present, the best theory is that it is related to fluctuating levels of HCG. Good pre-pregnancy nutrition seems to result in milder symptoms, but most cases merely require the use of anti-emetics although in many cases a bland diet is all that is required. However, there is no clear clinical approach that has been shown to be consistently effective.