Etiology of Nausea and Vomiting in Pregnancy
Although the fundamental trigger is pregnancy, NVP results from a complex interplay of influences that include endocrine, gastrointestinal, vestibular, and olfactory factors; possible genetic predisposition; and responses that are modified by behavioral cues, support (or lack thereof), and psychology. Proposed etiologies include high levels of β-hCG and estrogen due to the close temporal relationships between the average peaks of NVP and peak of β-hCG levels and the correlations between NVP and conditions with higher estradiol levels. Progesterone or corticosteroid deficiency related to the observed associations between NVP and lower levels of these hormones has been proposed. Thyroid dysfunction, infectious disease (specifically infection with Helicobacter pylori), and psychosocial, cultural, and psychogenic causes have all been theorized to play a role in the etiology of this condition. NVP is correlated with a transient biochemical hyperthyroidism related to β-hCG stimulation of the thyroid. Genetic causes are suggested by observations that NVP is more frequent in monozygotic twins; is more common in women whose siblings and mothers are affected; shows ethnic variation; and is correlated with other genetically determined conditions, such as taste sensation, anosmia, and glycoprotein receptor defects.[16,17]
An infectious origin is suggested by 14 published case-control studies that found a significant association between the presence of H pylori and HG. However, there are no directed studies addressing the efficacy of antibiotic treatments for H pylori in resolving the symptoms of HG. The most likely relationship is that women with H pylori and gastritis experience a more severe end of the NVP spectrum.
There is little evidence that NVP represents a psychiatric, conversion, or psychosomatic disorder; most studies suggesting this association are older and have flawed methodologies that call the findings into question. However, other studies show that NVP and HG can result in anxiety and depression, and it appears that the psychological responses to this physiologic condition can become entrenched and/or conditioned. This possibility is supported by evidence that psychological treatments (e.g., hypnosis) may help some individuals.[8,19,20]
In summary, the etiology of NVP is physiologic, and the cause of more extreme forms remains unclear. Therefore, assessment of the condition focuses on severity, and management is largely supportive.
J Midwifery Womens Health. 2009;54(6):430-444. © 2009 Elsevier Science, Inc.
Cite this: Evidence-Based Approaches to Managing Nausea and Vomiting in Early Pregnancy - Medscape - Oct 30, 2009.