Morning sickness, also called nausea and vomiting of pregnancy (NVP), is a
symptom of pregnancy that involves
nausea or
vomiting.[1] Despite the name, nausea or vomiting can occur at any time during the day.[2] Typically the symptoms occur between the 4th and 16th
week of pregnancy.[2] About 10% of women still have symptoms after the 20th week of pregnancy.[2] A severe form of the condition is known as
hyperemesis gravidarum and results in weight loss.[1][6]
The cause of morning sickness is unknown but may relate to changing levels of the hormone
human chorionic gonadotropin.[2] Some have proposed that morning sickness may be useful from an
evolutionary point of view.[1] Diagnosis should only occur after other possible causes have been ruled out.[3]Abdominal pain, fever, or
headaches are typically not present in morning sickness.[1]
Taking
prenatal vitamins before pregnancy may decrease the risk.[3] Specific treatment other than a bland diet may not be required for mild cases.[2][6][3] If treatment is used the combination of
doxylamine and pyridoxine is recommended initially.[3][4] There is limited evidence that
ginger may be useful.[3][7] For severe cases that have not improved with other measures
methylprednisolone may be tried.[3]Tube feeding may be required in women who are losing weight.[3]
Morning sickness affects about 70–80% of all pregnant women to some extent.[4][5] About 60% of women experience vomiting.[2] Hyperemesis gravidarum occurs in about 1.6% of pregnancies.[1] Morning sickness can negatively affect
quality of life, result in decreased ability to work while pregnant, and result in health-care expenses.[3] Generally, mild to moderate cases have no effect on the fetus, and most severe cases also have normal outcomes.[1] Some women choose to have an
abortion due to the severity of symptoms.[1] Complications such as
Wernicke encephalopathy or
esophageal rupture may occur, but very rarely.[1]
Signs and symptoms
About 66% of women have both nausea and vomiting while 33% have just nausea.[1] Symptoms of both nausea and vomiting will normally climax around 10 and 16 weeks of pregnancy, subsiding around 20 weeks.[8] However, after around 22 weeks, up to 10% of women continue to have lingering symptoms.[8]
Cause
The cause of morning sickness is unknown but may relate to changing levels of estrogen and the hormone
human chorionic gonadotropin.[2][9] Some have proposed that morning sickness may be useful from an
evolutionary point of view, arguing that morning sickness may protect both the pregnant woman and the developing embryo just when the fetus is most vulnerable.[1] Diagnosis should only occur after other possible causes have been ruled out.[3]Abdominal pain, fever, or
headaches are typically not present in morning sickness.[1]
Morning sickness is related to diets low in cereals and high in sugars, oilcrops, alcohol and meat.[11]
Pathophysiology
Hormone changes
Pathophysiology of vomiting in pregnancy
An increase in the circulating level of the hormone
estrogen.[12] However, there is no consistent evidence of differences in estrogen levels and levels of
bilirubin between women that experience sickness and those that do not.[13] Related to increased
estrogen levels, a similar form of nausea is also seen in some women who use
hormonal contraception or
hormone replacement therapy.
An increase in
human chorionic gonadotropin. It is probably not the HCG itself that causes the nausea. More likely, it is the HCG stimulating the maternal ovaries to secrete estrogen, which in turn causes the nausea.[14]
Defense mechanism
Morning sickness may be an
evolved trait that protects the fetus against
toxins ingested by the mother. Independent Scholar-Biologist Margie Profet from Seattle was one of the first to investigate the morning sickness-mystery. She argued that nausea and food aversions during pregnancy evolved to impose dietary restrictions on the mother in the early weeks of pregnancy, when the mother and the embryo are most immunologically vulnerable, to minimize fetal exposure to toxins such as mutagens and teratogens.[15] A woman and her embryo are very vulnerable to toxins during pregnancy. By reducing exposure to such chemicals, morning sickness reduces impairments on normal embryonic development and increases the reproductive success of the mother and survival success of both the mother and her offspring. Evidence in support of this theory includes:[16][11]
Morning sickness is very common among pregnant women, which argues in favor of its being a functional adaptation and against the idea that it is a
pathology.
Fetal vulnerability to toxins peaks at around 3 months, which is also the time of peak susceptibility to morning sickness.
There is a good correlation between toxin concentrations in foods, and the tastes and odors that cause revulsion.
Women who have no morning sickness are more likely to
miscarry.[17][18] This may be because such women are more likely to ingest substances that are harmful to the fetus.[19]
In addition to protecting the fetus, morning sickness may also protect the mother. A pregnant woman's
immune system is suppressed during pregnancy, presumably to reduce the chances of
rejecting tissues of her own offspring.[20] Because of this, animal products containing
parasites and harmful bacteria can be especially dangerous to pregnant women. There is evidence that morning sickness is often triggered by animal products including meat and fish.[21]
If morning sickness is a defense mechanism against the ingestion of toxins, the prescribing of
anti-nausea medication to pregnant women may have the undesired
side effect of causing birth defects or miscarriages by encouraging harmful dietary choices.[16]
Also, morning sickness is a defense mechanism because when analyzing embryonic growth, several critical periods are identified in which there is mass proliferation and cell division resulting in the development of the heart and central nervous system that are very sensitive. In that period, the fetus is most at risk from damage to toxins and mutagens. These developments occur through week 6-18 which is in the same time frame in which the most nausea and vomiting of pregnancy (NVP) occurs. This relationship between the time at which the embryo is most susceptible to toxins lines up exactly with when the most severe NVP symptoms are seen, suggesting that this NVP is an evolutionary response developed in the mother, to indicate the sensitivity of the fetus hence making her wary to her health and in turn protecting the fetus.[21]
Treatments
There is a lack of good evidence to support the use of any particular intervention for morning sickness.[7]
A recent review of studies has found
acupuncture to be safe and effective for NVP.[27]Acupressure applied at the acupuncture point PC6 with finger pressure or a nausea band has some evidence of effectiveness,[28][29][7] as does auricular (ear acupuncture).[7]
Some studies support the use of
ginger, but overall the evidence is limited and inconsistent.[3][7][9][30] Safety concerns have been raised regarding its
anticoagulant properties.[9][31][32][33]
In the late 1950s and early 1960s, the use of
thalidomide in 46 countries by women who were pregnant or who subsequently became pregnant resulted in the "biggest man‐made medical disaster ever," with more than 10,000 children born with a range of severe deformities, such as
phocomelia, as well as thousands of miscarriages.[34][35]
Thalidomide was introduced in 1953 as a tranquilizer, and was later marketed by the German pharmaceutical company
Chemie Grünenthal under the
trade nameContergan as a medication for
anxiety,
trouble sleeping, "tension", and morning sickness.[36][37] It was introduced as a sedative and medication for morning sickness without having been tested on pregnant women.[38] While initially deemed to be safe in pregnancy, concerns regarding birth defects were noted in 1961, and the medication was removed from the market in Europe that year.[36][39]
^
abEinarson TR, Piwko C, Koren G (2013-01-01). "Prevalence of nausea and vomiting of pregnancy in the USA: a meta analysis". Journal of Population Therapeutics and Clinical Pharmacology. 20 (2): e163–e170.
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ab"Pregnancy". Office on Women's Health. September 27, 2010. Archived from
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^Lagiou P, Tamimi R, Mucci LA, Trichopoulos D, Adami HO, Hsieh CC (April 2003). "Nausea and vomiting in pregnancy in relation to prolactin, estrogens, and progesterone: a prospective study". Obstetrics and Gynecology. 101 (4): 639–644.
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^Niebyl JR (October 2010). "Clinical practice. Nausea and vomiting in pregnancy". The New England Journal of Medicine. 363 (16): 1544–1550.
doi:
10.1056/NEJMcp1003896.
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^Holt RD, Nesse RM, Williams GC (April 1996). Why We Get Sick: The New Science of Darwinian Medicine. Knopf Doubleday Publishing. p. 983.
ISBN978-0679746744.
^
abNesse RM,
Williams GC (1996). Why We Get Sick (1st ed.). New York: Vintage Books. p. 290.
^Sherman PW, Flaxman SM (May 2002). "Nausea and vomiting of pregnancy in an evolutionary perspective". American Journal of Obstetrics and Gynecology. 186 (5 Suppl Understanding): S190–S197.
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