Morning Sickness (Nausea and Vomiting of Pregnancy)

What causes morning sickness?

The exact cause is not fully understood, but several factors combine:

• hCG (human chorionic gonadotropin): the pregnancy hormone made by the placenta. Its levels peak at around 9 to 12 weeks, matching the timing of the worst nausea. Conditions with higher hCG, such as twins and molar pregnancy, tend to cause more severe sickness.
• Estrogen and progesterone: rising levels slow stomach emptying and relax the valve at the top of the stomach.
• GDF15: research has identified this hormone, made by the placenta, as a key driver of nausea, with people who had low levels before pregnancy being more sensitive to it. This explains in part why some people are much more affected than others.
• Heightened sense of smell and changes in taste.
• Genetics: severe sickness runs in families.
• Thyroid stimulation: hCG can mildly stimulate the thyroid, causing temporary "gestational transient thyrotoxicosis", which is different from true thyroid disease, in severe cases.

Risk factors for more severe symptoms

• carrying twins or more
• previous severe morning sickness or hyperemesis
• family history (mother or sister)
• history of migraine or motion sickness
• carrying a female fetus (slightly higher risk)
• molar pregnancy

Symptoms

The core symptoms are nausea, retching and vomiting. Others include hypersalivation, food aversions, a heightened sense of smell, and fatigue. The patient-facing guide to morning sickness symptoms and home remedies covers what is normal week by week.

How severity is judged

Doctors use the PUQE score (Pregnancy-Unique Quantification of Emesis), which asks about the past 24 hours:

1. How long have you felt nauseated?
2. How many times have you vomited?
3. How many times have you retched without bringing anything up?

Scores are added to classify symptoms as mild, moderate or severe. Doctors also look at weight, signs of dehydration and how symptoms affect daily life.

Morning sickness vs hyperemesis gravidarum

Diagnosis

Morning sickness is diagnosed from symptoms in early pregnancy once other causes are excluded. For moderate or severe symptoms, tests may include:

• urine test for ketones (a sign the body is breaking down fat) and infection
• blood tests: electrolytes, kidney and liver function, thyroid function and blood count
• ultrasound to confirm gestational age and check for twins or a molar pregnancy

Doctors also consider other causes of vomiting in pregnancy: urinary infection, gastroenteritis, gallbladder disease, pancreatitis, migraine, and conditions such as preeclampsia or liver disease later in pregnancy.

Treatment

Treatment is step-wise, increasing until symptoms are controlled.

Step 1: Diet and lifestyle

Small, frequent, bland meals, protein snacks, sipping cold fluids between meals, avoiding triggers, ginger and acupressure bands. Switching from a prenatal vitamin with iron to a folic acid-only supplement temporarily can help.

Step 2: First-line medicine

Vitamin B6 (pyridoxine), with or without doxylamine (an antihistamine) is recommended first by ACOG. A combined prescription product is available. It can cause drowsiness.

Step 3: Additional medicines

If symptoms persist, a doctor may add other antiemetics, such as other antihistamines, metoclopramide, ondansetron or prochlorperazine. Their safety in pregnancy has been studied, and the choice depends on symptoms, timing in pregnancy and side effects. Acid-suppressing medicines help if reflux contributes.

Step 4: Fluids and hospital care

For dehydration, IV fluids with electrolytes and vitamins (including thiamine to prevent a rare brain complication from prolonged vomiting) are given, often in a day unit. Severe hyperemesis that does not respond may be treated with corticosteroids under specialist care, and rarely tube feeding.

Emotional support

Persistent sickness can cause anxiety, depression and isolation. Support from family, employers, health professionals and peer support organizations matters.

Complications

Ordinary morning sickness does not affect the baby. Severe, untreated hyperemesis can cause dehydration, electrolyte imbalance, weight loss, vitamin deficiencies, tears in the esophagus from retching, and psychological distress. It may be associated with lower birth weight if weight gain is poor. Prompt treatment greatly reduces these risks.

Outlook

Most people feel better by 16 weeks and nearly all by 20 weeks. About 1 in 10 have some nausea throughout pregnancy. Morning sickness often recurs in later pregnancies, so starting treatment early in a future pregnancy can make it milder.

Frequently asked questions

What causes morning sickness?

It is caused mainly by pregnancy hormones, especially hCG and the placental hormone GDF15, along with estrogen, slower stomach emptying and a heightened sense of smell. Genetics influence how sensitive you are, which is why severity varies so much between people.

What medicine is safe for morning sickness?

Vitamin B6 (pyridoxine), with or without doxylamine, is the recommended first-line treatment. If needed, doctors can prescribe other anti-sickness medicines that have been studied in pregnancy. Always check with your doctor before taking any medicine or herbal remedy while pregnant.

What is the difference between morning sickness and hyperemesis gravidarum?

Morning sickness is common nausea with occasional vomiting that allows you to eat and drink. Hyperemesis gravidarum is severe, persistent vomiting that causes dehydration and weight loss of 5% or more, and usually needs medicines, IV fluids and sometimes hospital care.

Does morning sickness come back in the next pregnancy?

Often, yes, though severity can differ. People who had hyperemesis gravidarum have a high chance of it recurring. Starting vitamin B6 and doxylamine early, or even before symptoms begin, may reduce severity.