Why do pregnant women experience nausea and vomiting?

From the Guidelines

Pregnant women experience nausea and vomiting due to hormonal changes, particularly increased levels of human chorionic gonadotropin (hCG) and estrogen, which typically occurs in the first trimester. The vomiting reflex serves as a protective mechanism, potentially helping to expel harmful substances that could affect fetal development. It may also encourage women to avoid certain foods that could be risky during pregnancy.

Causes of Nausea and Vomiting

• Hormonal changes, specifically increased levels of hCG and estrogen, are the primary cause of nausea and vomiting in pregnancy, as stated in the study by 1.
• Changes in GI motility and the relaxation of the lower esophageal sphincter due to increased progesterone levels also contribute to these symptoms.

Management of Symptoms

To manage symptoms:

1. Eat small, frequent meals
2. Stay hydrated
3. Avoid strong odors and triggering foods
4. Try ginger tea or supplements
5. Consider vitamin B6 (10-25 mg, 3 times daily) or doxylamine (12.5 mg at bedtime), as recommended by 1 and 1.

Severe Cases

For severe cases (hyperemesis gravidarum), consult a doctor. They may prescribe antiemetics like ondansetron or metoclopramide if needed, as suggested by 1 and 1.

Outcome

Most morning sickness resolves by the second trimester, but some women may experience it throughout pregnancy. While unpleasant, mild to moderate nausea and vomiting are generally not harmful to the fetus, according to the study by 1. Early treatment of nausea and vomiting of pregnancy may reduce progression to hyperemesis gravidarum, as stated in the study by 1 and 1.

From the Research

Causes of Nausea and Vomiting in Pregnancy

• The exact cause of nausea and vomiting in pregnancy is unknown 2, 3, 4, 5.
• Several studies suggest that the rise in human chorionic gonadotrophin concentration may be a contributing factor 2.
• However, one study found no relationship between the levels of human chorionic gonadotrophin and 17-hydroxyprogesterone and the incidence and severity of nausea and vomiting 6.
• Recent advances in genetic studies suggest a placental component to the aetiology, implicating common variants in genes encoding placental proteins and hormone receptors 4.

Prevalence of Nausea and Vomiting in Pregnancy

• Nausea and vomiting affect nearly 75% of pregnant women 3.
• Approximately 70-80% of pregnant women experience nausea and vomiting 5.
• Hyperemesis gravidarum, a severe form of nausea and vomiting, occurs in 0.3-10.8% of pregnant women 4.

Potential Triggers

• Metabolic and neuromuscular factors have been implicated in the pathogenesis of nausea and vomiting of pregnancy and hyperemesis gravidarum 5.
• Hormonal changes during pregnancy may also play a role in triggering nausea and vomiting 6.