The "Why" Questions. We could spend a whole month discussing the science of this. But, 'why' questions are often unanswerable. They can lead to great discussion and debate but not often to simple black and white answers. This frequent symptom of pregnancy just is one of the things expectant mothers must manage and live through with the help of their families and physicians.
Not known. Morning sickness in pregnancy doesn't have a known cause that has been discovered yet. Some believe it is related to the rapidly rising hormonal levels early in pregnancy, especially BhCG, estrogen, and progesterone.