When a woman becomes pregnant, her body releases several different hormones.  Like all drugs, hormones have a couple of unpleasant side effects like intestinal upsets.  It is believed that the hormone HCG is the one most likely responsible for morning sickness.  HCG stands for human chronic gonadotropin.  This hormone is made by the embryo soon after conception and is later made by the placenta.  Its role is to maintain the production of progesterone which is anther hormone that is critical for pregnancy.  Progesterone itself might be the cause of morning sickness as well.  The increase of the progesterone in the body relaxes the muscles in the uterus which prevents early childbirth.  But, as a result, progesterone might also relax the stomach and intestines, leading to excess acids in the stomach and therefore nausea and vomiting.  Another hormone that might be the cause of the nausea and vomiting that comes with the first stages of pregnancy is estrogen.  Estrogen is always present in a woman of child bearing years but it rises rapidly in early pregnancy.

It has been suggested that morning sickness can be caused by a vitamin B deficiency.  Taking a vitamin B6 supplement does seem to help ease the nausea in pregnant women.  But this does not mean that they have a vitamin deficiency.  Actually one study showed that there were no significant differences in the levels of B6 in women with morning sickness and those without.  So it is unclear why B6 is helpful.  There has also been some evidence that taking a multivitamin at the time of conception and in early pregnancy helps to prevent severe morning sickness as well.  But yet again, no one knows why.

On the other hand, the causes of morning sickness might not lie with the body’s hormone levels at all.  It might be triggered by other aspects of the body.  The cause of morning sickness might lie with an enhanced sense of smell and sensitivity to odors.  Certain aromas instantly trigger her gag reflex in pregnant women.  While it could have to do with the sense of smell it might also be a result of higher levels of estrogen.  Plus, some women just might have gastrointestinal tracts that are simply more sensitive to the changes of early pregnancy.  Also, some women might be predisposed to having nausea and vomiting during pregnancy as an abdominal response to stress.  Although there is no real evidence of this but, the more vomiting and nausea that is taking place, the more stressed a woman might become and therefore almost continuing the process.

Although the cause of morning sickness is still unclear, experts do know that, in most cases, it does not last throughout the entire pregnancy.  Typically, by the end of the third month when the blood level of some of these hormones levels off or begins to decline, so does the intestinal maladies that are caused by these hormones and therefore, the morning sickness begins to reside.