Morning sickness

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. Typically these symptoms occur between the 4th and 16th week of pregnancy. 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][3]

The cause of morning sickness is unknown but may be related to changing levels of the hormone human chorionic gonadotrophin.^[2] Some have proposed that it may be useful from an evolutionary point of view.^[1] Diagnosis should only occur after other possible causes have been ruled out.^[4] Abdominal pain, fever, or headaches are typically not present in morning sickness.^[1]

Taking prenatal vitamins before pregnancy may decrease the risk.^[4] Specific treatment other than a bland diet may not be required for mild cases.^[2][3][4] If treatment is used the combination of doxylamine and pyridoxine is recommended initially.^[4][5] Tentative evidence supports the use of ginger.^[4][6] For severe cases that have not improved with other measures methylprednisolone may be tried. Tube feeding may be required in women who are losing weight.^[4]

Morning sickness affects about 70-80% of all pregnant women to some extent.^[5][7] About 60% of women have 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.^[4] Generally mild to moderate cases have no effect on the baby. Most severe cases also have normal outcomes. Some women choose to have an abortion due to the severity of symptoms. Complications such as Wernicke encephalopathy or esophageal rupture may occur but are very rare.^[1]

Signs and symptoms

About 66% of women have both nausea and vomiting while 33% have just nausea.^[1]

Cause

The cause of morning sickness is unknown.^[1] While some have claimed it to be the result of psychological reasons this is not supported by evidence.^[1]

Nausea and vomiting may also occur with molar pregnancy.^[8]

Pathophysiology

Hormone changes

Pathophysiology of vomiting in pregnancy

• An increase in the circulating level of the hormone estrogen.^[9] 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.^[10] 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 progesterone relaxes the muscles in the uterus, which prevents early childbirth, but may also relax the stomach and intestines, leading to excess stomach acids and gastroesophageal reflux disease (GERD).
• An increase in human chorionic gonadotropin. It is probably not the human chorionic gonadotropin itself that causes the nausea. More likely, it is the human chorionic gonadotropin stimulating the maternal ovaries to secrete estrogen, which in turn causes the nausea.^[11]

Defense mechanism

Morning sickness may be an evolved trait that protects the baby against toxins ingested by the mother. Evidence in support of this theory, including:^[12][13]

• 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.^[14] This may be because such women are more likely to ingest substances that are harmful to the fetus.^[15]

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.^[16] 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.^[17]

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.^[12]

Treatments

There is unclear evidence about the effectiveness of home treatments for morning sickness.^[18]

Medications

A number of antiemetics are effective and safe in pregnancy including: pyridoxine/doxylamine, antihistamines (such as diphenhydramine), metoclopramide, and phenothiazines (such as promethazine).^[19][20] With respect to effectiveness it is unknown if one is superior to another.^[19] In the United States and Canada, the doxylamine-pyridoxine combination (as Diclegis in US and Diclectin in Canada) is the only approved pregnancy category "A" prescription treatment for nausea and vomiting of pregnancy.^[20]

Ondansetron may be beneficial, but there are some concerns regarding an association with cleft palate,^[21] and there is little high quality data.^[19] Metoclopramide is also used and relatively well tolerated.^[22] Evidence for the use of corticosteroids is weak.^[23]

Alternative medicine

There is tentative evidence that ginger may be useful; however, it is not clear.^[24][25] Safety concerns have been raised regarding its anticoagulant properties.^[26][27]

History

Thalidomide

Thalidomide was originally developed and prescribed as a cure for morning sickness in West Germany, but its use was discontinued when it was found to cause birth defects. The United States Food and Drug Administration never approved thalidomide for use as a cure for morning sickness.

References