During pregnancy, morning sickness starts at a different time for every woman, and some women do not even get morning sickness. In general, however, morning sickness starts between the fourth and the sixth week of pregnancy; if a pregnant woman makes it past the sixth week without experiencing morning sickness, there is a good chance she will not feel the effects of it throughout the pregnancy. Morning sickness generally does not begin prior to the fourth week of pregnancy, but for many women it is the first sign from their bodies that they are pregnant.
Morning sickness starts most often in the first trimester, and generally ends between the twelfth and sixteenth week of pregnancy. In some cases, however, it lasts for the entire duration of the pregnancy. In addition, it is a misconception that "morning" sickness only occurs in the morning; though it is fairly common just after waking up, women experiencing this type of sickness throughout pregnancy often experience it all day or even during the night. Experts are divided as to whether morning sickness is a sign of a healthy pregnancy; some say it is, while others say it makes no difference.
In most cases, once morning sickness starts it does not affect the health of the mother or the unborn child. Only if the nausea and vomiting become so severe and persistent that the pregnant woman is not gaining weight does it become a problem. In that case, a doctor may be able to prescribe medication that can help with morning sickness. If the morning sickness is mild, however, some women find that they can prevent or minimize it by taking a B6 supplement, taking some ginger pills or drinking some ginger ale, eating small meals throughout the day to prevent blood sugar dips, or eating some plain crackers before getting out of bed in the morning. Getting regular exercise throughout the pregnancy may be able to alleviate morning sickness as well.
Any specific concerns about when morning sickness starts or ends should be directed to a doctor. This is especially true if morning sickness suddenly appears later in the pregnancy, for example. It is generally nothing to worry about, but it is still helpful to mention any specific changes in the body to one's doctor throughout the pregnancy. The cause of morning sickness is generally believed to be the significant hormonal changes that occur during pregnancy.