There is a huge variation in how bad the symptoms of morning sickness are. Some women just feel queasy in the morning, and feel fine by noontime. They are able to perform their daily activities. Others suffer from nausea and vomiting that can last all day. They find ordinary work during pregnancy almost impossible.
Some women have symptoms of morning sickness within days of conception.
But the average time from the last menstrual period to the start of nausea is about 5 weeks. A woman with high levels of HCG is more likely to have morning sickness. High levels of HCG are seen in multiple pregnancies, such as twins and triplets. A woman who has had morning sickness in a previous pregnancy is more likely to have it again. Increased HCG levels can be caused by a tumor of the placenta called hydatidiform mole.