Morning Sickness - Causes

Causes

Proximate causes of pregnancy sickness include:

• An increase in the circulating level of the hormone estrogen. Estrogen levels may increase by up to a hundredfold during pregnancy. However, there is no consistent evidence of differences in estrogen levels and levels of bilirubin between women that experience sickness and those that do not.
• Low blood sugar (hypoglycemia) due to the placenta's draining energy from the mother, though studies have not confirmed this.
• An increase in progesterone relaxes the muscles in the uterus, which prevents early childbirth, but may also relax the stomach and intestines, leading to excess stomach acids and gastroesophageal reflux disease.
• An increase in human chorionic gonadotropin. It is probably not the human chorionic gonadotropin itself that causes the nausea. More likely, it is the human chorionic gonadotropin-stimulating the maternal ovaries to secrete estrogen, which in turn causes the nausea.
• An increase in sensitivity to odors, which overstimulates normal nausea triggers.
• An increase in bilirubin levels due to increased liver enzymes.

Note that Gastroesophageal reflux disease can also be caused by pregnancy, and may result in nausea and vomiting.