Here are some theories of where HG may come from:
What causes hyperemesis gravidarum remains unknown despite active research.
The more popular theories are categorized into 3 areas:
Elevated levels of human chorionic gonadotropin (hCG) or a component of this hormone may play a role in inducing vomiting. This hormone has been shown to be in women with hyperemesis gravidarum.
Thyrotoxicosis or hyperthyroidism is also believed to be associated with hyperemesis gravidarum. A portion of the hCG hormone, called beta-hCG, is thought to stimulate an increase in serum thyroid hormones, which are associated with hyperemesis in pregnant women. It is not known whether this is a cause or effect of hyperemesis.
Another hormone thought to be the involved is serotonin. This is a brain chemical that affects both the central nervous system and the gastrointestinal (GI) tract. These effects are believed to induce vomiting. During pregnancy, the upper GI tract may slow down and thus contribute to increased nausea and vomiting. Several studies have shown that this slowdown in the GI tract is increased in pregnant women with severe vomiting.
Helicobacter pylori bacteria that live in the intestinal tract may cause the development of peptic ulcer disease. These bacteria are found in a greater percentage among pregnant women and greater still in those with hyperemesis gravidarum. Antibiotics are used to treat all these conditions.
Although the idea is controversial, some researchers think the condition may be a woman's psychological reaction against the pregnancy and might arise from conflict within the family and her home environment. In these cases, counseling has been used.