From the Guidelines
Nausea and vomiting of pregnancy (NVP) is primarily caused by elevated levels of human chorionic gonadotropin and estrogen, as well as changes in GI motility.
Causes of NVP
- Elevated levels of human chorionic gonadotropin and estrogen are commonly associated with NVP 1
- Changes in GI motility, including delayed gastric emptying, can contribute to NVP 1
- Progesterone can have an inhibitory effect on GI and small bowel motility, leading to delayed gastric emptying 1
Pathophysiology
NVP usually begins at 4-6 weeks, peaks at 8-12 weeks, and subsides by week 20 1. The severity of vomiting during pregnancy can be quantified with a scoring system, such as the Motherisk Pregnancy Unique Quantification of Emesis score (Table 1) 1.
Relationship to Hyperemesis Gravidarum
Hyperemesis gravidarum (HG) is an intractable form of NVP that can lead to dehydration, weight loss, and electrolyte imbalances 1. The cause of HG is not fully understood, but it has been associated with hyperthyroid disorders, elevated levels of human chorionic gonadotropin and estrogen, and previous molar pregnancy 1.
Clinical Implications
Early treatment of NVP may reduce progression to hyperemesis gravidarum 1. Treatment is guided by the severity of symptoms and may require a multidisciplinary team approach involving obstetricians, nutritionists, psychologists, and gastroenterologists 1.
From the Research
Causes of Nausea and Vomiting of Pregnancy (NVP)
- The exact etiology and pathogenesis of NVP are poorly understood and are most likely multifactorial 2
- Some theories for the etiology of NVP include:
- Psychological predisposition
- Evolutionary adaptation
- Hormonal stimuli, such as human chorionic gonadotrophin (hCG) 3
- Helicobacter pylori infection
- The "prophylaxis" hypothesis suggests that NVP serves a beneficial function by expelling foods that may contain harmful toxins and microorganisms and triggering aversions to such foods throughout pregnancy 4
- The "by-product" hypothesis suggests that NVP is a nonfunctional by-product of conflict over resource allocation between the pregnant woman and the embryo, but this hypothesis is not fully consistent with available data 4
- Epidemiologic studies suggest that pregnancies accompanied by NVP have better outcomes than asymptomatic pregnancies, and NVP may have a protective effect against spontaneous abortions and congenital malformations 3, 5, 6
- Alterations in smell and taste may precipitate NVP, and the intimate connection between immunogenetic identity, chemoidentity, and chemocommunication by olfactory mechanisms suggests a relationship between maternal symptoms and maternal accommodation of paternal antigens contained in the fetoplacental unit 5