What is morning sickness
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Morning Sickness (Nausea and Vomiting of Pregnancy)
Morning sickness is the common term for nausea and vomiting of pregnancy (NVP) - one of the most frequent symptoms of early pregnancy, affecting 70-80% of pregnant women.
Despite the name, it is limited to the morning in less than 2% of women - symptoms typically persist throughout the day and night. - Yamada's Textbook of Gastroenterology
When Does It Occur?
- Starts within 4 weeks after the last menstrual period in most patients
- Peaks between 10 and 16 weeks of gestation
- Usually resolves by 20 weeks
- About 10% of women remain symptomatic beyond 22 weeks
- Yamada's Textbook of Gastroenterology
Causes and Risk Factors
The exact cause is not fully understood, but several factors contribute:
Hormonal:
- Rising levels of human chorionic gonadotropin (hCG) are strongly linked - symptoms parallel hCG levels, which peak in the first trimester
- Estrogen and progesterone affect esophageal and gastric motility, reducing lower esophageal sphincter tone and slowing stomach emptying
Other contributing factors:
- Helicobacter pylori infection (may worsen symptoms by affecting gastric motility)
- Altered gastric rhythmic activity and esophageal peristalsis
Risk factors for NVP include:
- Younger maternal age, first pregnancy (nulliparity)
- Low education level, obesity, multiple gestation (twins/triplets)
- Personal history of motion sickness or migraines
- Family history of NVP
- Sleisenger & Fordtran's Gastrointestinal and Liver Disease
Symptoms
- Nausea, with or without vomiting, at any time of day
- Excess salivation (ptyalism)
- GERD-like symptoms
- Fatigue
In most cases, vital signs are normal and symptoms are self-limiting. Mild to moderate NVP does not harm the baby.
When It Becomes Serious: Hyperemesis Gravidarum (HG)
Severe NVP is called hyperemesis gravidarum (HG), affecting 0.3-3% of pregnancies. HG is defined by:
- More than 3 episodes of vomiting per day
- Ketonuria (ketones in urine)
- Weight loss of more than 3 kg or 5% of pre-pregnancy weight
- Dehydration and electrolyte imbalances (hypokalemia, metabolic alkalosis)
HG is the most common cause of hospital admission in early pregnancy and the second most common reason for hospitalization during pregnancy overall (after preterm labor). - Goldman-Cecil Medicine
Diagnosis
Morning sickness is mainly a clinical diagnosis based on pregnancy confirmation and symptom onset. For suspected HG, investigations include:
- Serum electrolytes, BUN, creatinine, hematocrit
- Urinalysis (ketonuria, raised specific gravity)
- Pelvic ultrasound (to rule out multiple gestation or trophoblastic disease)
- Liver function tests (abnormal in up to 40% of hospitalized HG patients)
- Yamada's Textbook of Gastroenterology
Note: If symptoms start after 8 weeks from the last menstrual period, other causes (e.g., GERD, peptic ulcer disease, small bowel obstruction) should be investigated.
Treatment
Non-pharmacological (first-line):
- Small, frequent meals; avoid fatty or spicy foods
- Ginger (shown to have some antiemetic effect in clinical studies)
- Rest; avoid triggers such as strong odors
- Adequate hydration
Pharmacological:
- Vitamin B6 (pyridoxine) - safe first-line option, reduces nausea
- Doxylamine (antihistamine) - combined with B6 as the standard first-line drug treatment; H1-antihistamines generally safe in pregnancy
- Antihistamines (e.g., promethazine, dimenhydrinate)
- Metoclopramide, ondansetron - for more severe symptoms
- Katzung's Basic and Clinical Pharmacology
For HG:
- IV fluid rehydration and electrolyte correction
- Parenteral antiemetics
- Nutritional support (enteral/parenteral feeding in severe cases)
- Thiamine (Vitamin B1) supplementation to prevent Wernicke's encephalopathy
Important warning: Thalidomide was historically given for morning sickness but caused severe fetal limb abnormalities and is absolutely contraindicated in pregnancy. Cannabis/marijuana is also not recommended - despite being increasingly used for nausea, ACOG advises against it due to unknown fetal risks. - Lippincott Illustrated Reviews: Pharmacology; Creasy & Resnik's Maternal-Fetal Medicine
Summary Table
| Feature | Morning Sickness (NVP) | Hyperemesis Gravidarum (HG) |
|---|---|---|
| Frequency | 70-80% of pregnancies | 0.3-3% of pregnancies |
| Vomiting | Occasional | >3x/day |
| Weight loss | Minimal | >3 kg or >5% body weight |
| Dehydration | No | Yes |
| Hospitalization | Rarely needed | Often needed |
| Resolution | Usually by 20 weeks | May persist longer |
Morning sickness, while very unpleasant, is generally a normal part of pregnancy. If vomiting becomes persistent, you are losing weight, or you cannot keep fluids down, prompt medical evaluation is important to rule out HG and prevent complications.
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