Health Questions and Answers

Question: What is the etiology of hyperemesis?


  • The causes of NVP/HG remain poorly understood. The major theories of causation involve hormonal variables, abnormal gastric motility, and psychosocial stress.
  • Hormonal variables: Some women with hyperemesis appear to be hyperthyroid, which is associated with higher levels of circulating human chorionic gonadotropin (hCG) or higher biological activity of hCG. There has also been some association between progesterone and delayed gastric emptying. A more precise association has not been elucidated.
  • Gastric motility: Some studies have demonstrated decreased gastric motility by electrogastrography to be associated with higher levels of nausea, but others have shown no difference in motility between symptomatic and asymptomatic patients. There has also been discussion of CNS changes, especially in the “vomiting center”(including the dorsal motor nucleus of the vagus nerve) in response to hormonal triggers as the etiology.
  • Psychosocial stress: Theories describe three potential processes-conversion disorder/somatization, heightened perception of sensations by the mother resulting in vomiting as a conditional response, and an inability of the mother to respond to life stress. There are limited data to support any of these associations.

Reference: Creasy RK, Resnik R: Maternal Fetal Medicine, 4th ed. Philadelphia, WB Saunders, 1999, pp 122-131.

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