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Causes of NVP. Risk factors for morning sickness. Pathogenesis. Clinical classification of NVP. Diagnostics
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Causes of NVP
The cause of nausea and vomiting in pregnancy is unclear and probably has many contributing factors, although it is most likely related to hormonal changes because of gestation. Symptoms can be more severe in women carrying twins.
Before assuming a diagnosis, it is important to rule out other reasons for vomiting in a pregnant woman.
Women who have previously suffered from nausea and vomiting in pregnancy are more likely to have symptoms in a subsequent pregnancy.
Risk factors for morning sickness
These include:
- nausea and vomiting in a previous pregnancy
- a family history of nausea and vomiting in pregnancy, or morning sickness
- a history of motion sickness – for example, in a car
- a history of nausea while using contraceptives that contain estrogen
- obesity – a body mass index (BMI) of 30 or more
- stress
- multiple pregnancies, such as twins or triplets
- first pregnancy
It has been also proved, that NVP is more common in younger women, primigravidas, non-smokers. Risk factors for NVP include being pregnant with a female fetus, uincreased placental mass (for example, an advanced molar gestation or multiple gestations). Location of the corpus luteum may also serve as risk factor for NVP. Ultrasound studies have shown that pregnant women experience more nausea and vomiting when the corpus luteum is present in the right ovary. This may be due to differences in venous drainage between the left and right ovary and a higher concentration of sex steroids when the corpus luteum is on the right side. A higher daily intake of total fat, especially saturated fat, prior to pregnancy increases the risk of NVP occurance.
Location of the corpus luteum may also serve as risk factor for NVP. Ultrasound studies have shown that pregnant women experience more nausea and vomiting when the corpus luteum is present in the right ovary. This may be due to differences in venous drainage between the left and right ovary and a higher concentration of sex steroids when the corpus luteum is on the right side.
NVP has been associated with low income levels and part-time employment status. Housewives have also been found to be at increased risk while women with “white collar occupations” appear to be protected.
Pathogenesis
Although the exact pathogenesis of NVP is unknown, it is widely accepted that gestational vomiting results from various metabolic and endocrine factors, many of placental origin. The most implicated factor is human chorionic gonadatropin (hCG). Higher urinary hCG and serum hCG levels have also been found in women with NVP compared to those who are asymptomatic.
The ovarian hormones, estrogen and progesterone, have also been implicated in the pathogenesis of NVP and HG. States of high estrogen concentration (misscarriages, high maternal body mass index) have been associated with a higher incidence of NVP, ecpesially severe forms. Estrogen is thought to contribute to NVP by stimulating the production of nitric oxide via nitrogen oxidase synthetase, which in turn relaxes smooth muscle slowing gastric intestinal transit time and gastric emptying.
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Hence, progesterone may also have a role in NVP, because progesterone decreases smooth muscle contractility and may alter gastric emptying and lead to increased nausea and vomiting. The role of placental prostaglandin E2 (PGE2) has also been evaluated in the pathogenesis of NVP due to its effect on gastric smooth muscle. hCG stimulates placental PGE2 and like hCG peaks between 9 and 12 weeks of gestation.
Other hormones including thyroid-stimulating hormone, growth hormone, prolactin, adrenocortical-stimulating hormone, cortisol, luteinizing hormone, and follicle-stimulating hormone have also been evaluated and are not considered to contribute to the pathogenesis of NVP.
Despite these facts the cause of nausea and vomiting in pregnancy has not been identified. It may have a genetic component. Some studies have suggested that Helicobacter pylori infection may play a role in hyperemesis, but the data are inconclusive.
The standard recommendation to take prenatal vitamins for 3 months before conception may reduce the incidence and severity of nausea and vomiting in pregnancy.
Clinical classification of NVP
The severity of these symptoms can vary. The experience of NVP falls on a continuum from mild " morning sickness" to hyperemesis gravidarum (HG).
Simple vomiting (mild degree)
Moderate vomiting (moderate degree)
Hyperemesis gravidarum (pernicious vomiting of pregnant, severe form)
Diagnostics
In addition to a pregnancy test, no specific laboratory studies are recommended for the diagnosis of NVP.
Other tests, however, may be useful to exclude other causes of nausea and vomiting, to assess the degree of homeostasis failure, and to choose the optimal treatment option. The surveys used to diagnoseNVP:
• CBC
• Urinalysis
• Fasting serum glucose
• Serum bHCG
• Routine coagulation tests
• Electrolytes
• Serum total protein
• Liver enzymes
• Amylase/Lipase
• Thyroid-stimulating hormone (TSH)
• US of abdominal cavity, uterus, fetus, etc
• US of liver, gallbladder, or kidney based on symptoms
Simple vomiting (syn.: a mild form of vomiting, morning sickness, emesis gravidarum).
The patient complains of nausea and occasional vomiting on getting up in the morning. High vomiting is so common in early terms of pregnancy (about 50%) that it is considered as a symptom of pregnancy. It may, however, occur at other time of the day, but less than 5 times daily. It does not produce any impairment of health or restrict the normal activities of the woman. The features disappear with or without treatment by the 12-14th week of pregnancy. The altered hormonal and immune states are responsible for initiation of manifestation, which is probably aggravated by the neurogenic factor.
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