Morning sickness is one of the first symptoms a woman experiences that indicates she is pregnant, and it is no fun for the 75 percent of women who endure it. Despite its name, however, morning sickness can happen in the afternoon, evening, or late night hours. In fact, for an unlucky few, it can last all day long. Most pregnant women experience some degree of nausea, and about 33 percent experience daily vomiting. Usually starting a couple of weeks into the pregnancy, morning sickness tends to last throughout the entire first trimester, or 14 weeks.