Psychosocial stressors have been implicated, with higher NVP rates reported in unmarried women, those with unwanted or unplanned pregnancies, immigrants, and those living in crowded situations.21 NVP also is more frequent among women who experience emotionally disturbing events or interpersonal, economic, or occupational difficulties during pregnancy.22 Physical symptoms may provide secondary gain in attention and sympathy and a time-out from stressful home events.14
These psychosocial theories are poorly supported by data, but some clinicians may still believe NVP has a psychogenic cause. Lennane and Lennane23 proposed in 1973 that this perception may result from gender bias because:
- most conditions believed to have psychogenic causes affect women more than men
- the belief that NVP is psychogenic has been perpetuated primarily by male authors.
They argued that sexual prejudice may prevent women from receiving necessary symptomatic treatment and impede research into the cause of NVP.23
Gender bias continues to be found in the diagnosis of women with physical complaints. In 2006, Chiaramonte and Friend24 found strong, consistent gender bias among medical students and residents when evaluating women who reported coronary disease symptoms during stressful life events.
Organic theories view NVP as multifactorial, with contributions from evolution and multiple organ systems. Endocrine, vestibular, gastrointestinal, and CNS contributions have been described, but none have solved NVP’s etiologic mystery.
Evolutionary. NVP may provide an evolutionary advantage by protecting the embryo and mother. This theory states that potential toxins are present in many foods, especially if eaten in large quantities. NVP prevents the pregnant woman from eating very much and harming the embryo. Below-average miscarriage rates are seen in women with NVP.1,2,25
And because a woman’s immune system is depressed during pregnancy, NVP may be advantageous for the mother by limiting her ingestion of potential toxins.25
Endocrine. Human chorionic gonadotropin (hCG), estrogens, progesterone, and leptin, as well as adrenal cortex insufficiencies have been investigated for a role in NVP. Only hCG has shown clear evidence of an association, and some researchers believe it is the most likely cause of NVP.20
NVP rates are higher in pregnancies with elevated hCG. Molar and multiple-gestation pregnancies—each associated with elevated hCG—are complicated more frequently with the severest form of NVP.20,26 Conversely, NVP is less common in women who smoke, which is associated with lower hCG.26
During pregnancy, actions of hCG stimulate the thyroid. Hyperstimulation, leading to transient hyperthyroidism, has been implicated in NVP development.20,26 Symptom severity and the degree of thyroid stimulating hormone (TSH) suppression are closely correlated.26
Elevated hCG levels, hypersensitive TSH receptors, and the presence of a hyperactive hCG isoform have been proposed.20
Gastrointestinal disorders are believed to be involved in the pathogenesis of persistent NVP. Women with NVP usually lack structural or mucosal abnormalities and have normal endoscopic upper GI evaluations. They may, however, have disorders of the stomach’s neuromuscular function. Severe cases of gastric dysrhythmias and abnormalities of gastric tone may lead to gastroparesis.27
Stomach motility in pregnancy is influenced by neurohormonal changes, specifically in estrogen and thyroid hormones. Gastric motility abnormalities—evaluated by electrogastrography (EGG)—have been associated with NVP symptoms and normal EGGs with the absence of symptoms. Some women who had NVP and abnormal EGGs were retested after delivery when symptom-free and found to have normal myoelectric EGG patterns.27
Helicobacter pylori also may be involved in NVP, and at least 1 study found active H pylori infection and HG to be highly correlated. Pregnancy is not believed to predispose to H pylori infection, but active infection compounded by pregnancy’s hormonal changes may exacerbate NVP.28
NVP and motion sickness share many features, suggesting that NVP treatment could be targeted if a vestibular disorder could be discovered.29 Abnormal electroencephalography—particularly generalized slowing—that is not present in asymptomatic pregnant women has been reported in women with NVP.30
CNS contributions. Persistent NVP may be a learned behavior,24 a view based on findings of anticipatory nausea and vomiting in chemotherapy patients. Through conditioning, a pregnant woman may associate her physical symptoms with elements in her life that maintain the cycle of nausea and vomiting.31
Treating psychological symptoms
Brief psychotherapy to identify and correct sources of anxiety in pregnancy may alleviate a patient’s nausea and vomiting.32
- Progressive muscle relaxation training, often combined with guided imagery, can decrease nausea and vomiting associated with chemotherapy and may prevent anticipatory symptoms by decreasing anxiety.
- Systematic desensitization is successful in most chemotherapy patients who try it. In this technique, relaxation is counter-conditioned as a response to stimuli known to elicit symptoms.31