Hyperemesis Gravidarum
HG High-yield Verified · Sep 2026Hyperemesis gravidarum is severe, persistent nausea and vomiting in pregnancy that impairs the ability to maintain adequate oral intake of food and fluids, causing significant weight loss (typically more than 5% of prepregnancy body weight), dehydration, electrolyte disturbances and ketonuria. It is a clinical diagnosis of exclusion.
Morning sickness is common; hyperemesis gravidarum is not ordinary morning sickness. When a pregnant patient cannot keep food or fluids down, loses weight, and shows ketones in the urine, she is starving and dehydrated — and losing potassium. The nurse weighs, checks orthostatic signs and labs, runs IV fluids and electrolytes, and makes sure thiamine goes in before or with any dextrose. Confusion, abnormal eye movements or an unsteady gait mean Wernicke encephalopathy — an emergency.
What’s going wrong in the body
The normal physiology, where it fails, and why the body’s compensation backfires.
01 Pregnancy hormones and gut changes — cause still unclear
"Hyperemesis gravidarum represents the severe end of the spectrum of nausea and vomiting of pregnancy, a condition that affects the majority of pregnant individuals to varying degrees." Unlike milder nausea, it "severely impairs the individual's ability to maintain adequate oral intake of food and fluids, resulting in associated symptoms including significant weight loss (typically >5% of prepregnancy body weight), dry mouth, constipation, fatigue, and inability to perform daily activities."
Why it happens. "The precise mechanisms underlying hyperemesis gravidarum remain unclear, though current understanding suggests a multifactorial etiology. Hypotheses include abnormal hormonal responses, particularly involving hCG, along with possible genetic, immunological, and gastrointestinal contributions." hCG is implicated because of "the close correlation between peak hCG levels and the timing of symptom onset, as well as its thyroid-stimulating effects" — yet "hCG alone cannot account for the condition." "Notably, elevated progesterone levels reduce the motility of the gastrointestinal tract."
Not psychological. Depression and anxiety often coexist, but "these may be more likely sequelae of the illness rather than contributing causes."
Timing. "The onset of symptoms most commonly occurs around 6 weeks of gestation and resolves between 16 and 20 weeks of gestation; in approximately 20% of cases, symptoms continue throughout the pregnancy" (StatPearls). OWH: "Usually, women with HG begin to feel better by the 20th week of pregnancy. But some women vomit and feel nauseated throughout all three trimesters."
02 Vomiting drains acid, potassium and water
Labs. "Common laboratory abnormalities in hyperemesis gravidarum reflect the effects of prolonged vomiting and reduced nutritional intake, often revealing signs of dehydration and electrolyte imbalance, eg, elevated blood urea nitrogen (BUN) or creatinine, hyponatremia, and hypokalemia." "Ketonuria, an indicator of starvation due to fat metabolism, is frequently present."
[ALK] Metabolic alkalosis (the physiology of vomiting in general). "Stomach fluids are highly acidic at a pH of approximately 1.5 to 3.5." "Therefore, the large volume loss of gastric secretions will correlate with a loss of hydrogen chloride, an acidic substance, leading to a relative increase in bicarbonate in the blood, thus driving alkalosis. Losses can occur pathologically via vomitus or nasogastric suctioning." Volume loss and potassium and chloride depletion keep it going and cause "decreased myocardial contractility, arrhythmias, decreased cerebral blood flow, confusion, increased neuromuscular excitability" (StatPearls).
Complications of the losses. HG "often leads to dehydration, electrolyte disturbances, and, less frequently, severe complications, eg, acute kidney injury, cardiac arrhythmias, and neuromuscular symptoms." "Signs of hemorrhage or abnormal bleeding can occur due to vitamin K deficiency."
03 Thiamine runs out — Wernicke encephalopathy
[WE] Weeks of poor intake deplete thiamine (vitamin B1); StatPearls names "severe malnutrition, hyperemesis gravidarum, prolonged parenteral nutrition" among at-risk groups. "Thiamine is generally administered before or concurrently with glucose solutions because glucose oxidation can deplete thiamine, thereby exacerbating the neurological symptoms of Wernicke encephalopathy."
Presentation. "One of the most serious consequences is Wernicke encephalopathy, caused by thiamine deficiency, presenting with confusion, eye movement abnormalities, and gait disturbances, with other manifestations including nystagmus and memory impairment." "The complete triad appears infrequently, and clinicians should presume Wernicke encephalopathy in at-risk patients with compatible findings."
Why it is urgent. "Early recognition is critical because delayed treatment can result in irreversible cognitive impairment, disability, or death." "Administer parenteral thiamine before or concurrently with any glucose or nutritional support in at-risk patients, without awaiting laboratory or imaging confirmation." "In pregnancy complicated by hyperemesis, emphasize early supplementation with thiamine and prenatal vitamins."
Causes & risk factors
Modifiable factors are teaching targets — the patient can act on them.
Signs & symptoms
Each finding tied to the mechanism that produces it — and the triage it calls for.
Diagnostics
Complications
Medications for this condition
Why each class is prescribed here — every card links to its full pharmacology page.
IV fluids, electrolytes and thiamine. "Initial inpatient management focuses on stabilizing the patient through aggressive intravenous (IV) fluid therapy and correcting electrolyte abnormalities. Thiamine and multivitamin supplementation are crucial to prevent neurological complications." Thiamine goes before or with any dextrose — "Carbohydrate administration increases thiamine requirements and can worsen thiamine deficiency." Correct potassium and magnesium; low levels also call for ECG monitoring if ondansetron is used. When feeding restarts, watch phosphate, potassium and magnesium for refeeding syndrome.
Doxylamine–pyridoxine (Diclegis) — "indicated for the treatment of nausea and vomiting of pregnancy in women who do not respond to conservative management," but "DICLEGIS has not been studied in women with hyperemesis gravidarum." Take on an empty stomach, swallowed whole, daily (not as needed); causes somnolence — no driving until cleared and no alcohol or other CNS depressants; "Women should not breastfeed while using DICLEGIS." Ondansetron — off-label in pregnancy; StatPearls: "It should only be used when other medications have been trialed and failed." Label: birth-defect studies "have reported inconsistent findings"; QT prolongation (ECG monitoring is recommended with "electrolyte abnormalities (e.g., hypokalemia or hypomagnesemia)"); serotonin syndrome, especially with other serotonergic drugs.
Beyond medications
- Diet — OWH: "Dry, bland foods and fluids together is the first line of treatment." MedlinePlus (nausea): "Eat bland foods; stay away from spicy, fatty, or salty foods"; "drink small amounts of clear liquids often"; "Avoid strong smells, since they can sometimes trigger nausea and vomiting."
- Hospital care — StatPearls: "most experts recommend admission for persistent vomiting despite oral antiemetics, patients who require IV fluids, who have conditions necessitating close monitoring, or abnormal evaluation findings." OWH: "Many women with HG have to be hospitalized so they can be fed fluids and nutrients through a tube in their veins."
- Nutrition support — "Enteral nutrition is typically the preferred method for nutritional support, with nasogastric feeding often used first"; parenteral nutrition "carries increased risks, including infection and thrombosis."
- Micronutrients — "Key nutrients include thiamine (vitamin B1), iron, calcium, magnesium, vitamin D, and iodine," checked daily until stable, then weekly as an outpatient.
- Emotional support — screen for anxiety, depression and PTSD; involve dietitians, pharmacists and mental-health support.
- Refractory HG — StatPearls: mirtazapine, olanzapine or short-term methylprednisolone "may be considered"; corticosteroids "before 10 weeks gestation is discouraged due to possible risks of fetal abnormalities."
Nursing considerations
The RN-specific layer — each action paired with the reason it matters.
How a real nurse thinks
The clinical-judgment loop, worked for a typical presentation — reasoning, not reference.
- 1 Recognize cues
Persistent vomiting, weight loss about 6%, tachycardia, orthostatic dizziness, dry mucosa, ketonuria 3+, hypokalemia, hyponatremia, rising BUN.
- 2 Analyze cues
This is hyperemesis gravidarum with dehydration and starvation ketosis, not ordinary morning sickness. Vomiting loses acid and potassium; low potassium raises arrhythmia risk and ondansetron QT risk. Weeks of poor intake put her at risk of thiamine deficiency — and dextrose without thiamine can precipitate Wernicke encephalopathy.
- 3 Prioritize
Restore fluid volume and potassium, and give thiamine before or with the dextrose.
- 4 Generate solutions
Start IV fluids; give thiamine first or with the dextrose; replace potassium; check ECG before ondansetron given the low potassium; strict I&O and daily weights; neuro checks; dietitian and emotional support.
- 5 Take action
Thiamine is given as the fluids start; potassium replacement runs; the nurse reports K 3.0 before ondansetron and an ECG is obtained per order. Weight, I&O and urine ketones are tracked, and eye movements and gait are checked each shift.
- 6 Evaluate
By day 2 HR is 88, she is voiding pale urine, ketones are trace, and K is 3.8. She tolerates dry crackers and small sips of clear fluids. Neuro checks stay normal.
Scenario — you’re the nurse
Work each question before revealing the answer. Rationales explain the wrong options too.
A 26-year-old at 10 weeks' gestation (first pregnancy) has vomited 8–10 times a day for 5 days and cannot keep water down. Her prepregnancy weight was 60 kg; today she weighs 56.5 kg. Her mother had HG.
Q1 Select all that apply Which findings distinguish hyperemesis gravidarum from ordinary nausea and vomiting of pregnancy? Select all that apply. - A. Weight loss of more than 5% of prepregnancy weight
- B. Ketones in the urine
- C. Nausea in the first trimester
- D. Inability to keep food or fluids down
- E. Hypokalemia
Reveal answer & rationale
Q2 Multiple choice An IV of dextrose-containing fluid and IV thiamine are both ordered. What should the nurse do? - A. Start the dextrose first to correct low energy, then thiamine tomorrow
- B. Give the thiamine before or with the dextrose
- C. Hold the thiamine until a thiamine level is back
- D. Give the thiamine only if confusion develops
Reveal answer & rationale
Q3 Select all that apply Which new findings should the nurse treat as an emergency suggesting Wernicke encephalopathy? Select all that apply. - A. New confusion
- B. Nystagmus
- C. Unsteady gait
- D. Mild fatigue
- E. Dry lips
Reveal answer & rationale
Q4 Multiple choice Ondansetron is due. The patient's potassium is 3.0 mEq/L. What is the best nursing action? - A. Give it — electrolytes do not affect ondansetron
- B. Report the low potassium and follow orders for ECG monitoring and potassium replacement
- C. Refuse to give ondansetron because it is contraindicated in pregnancy
- D. Double the dose because vomiting is severe
Reveal answer & rationale
Q5 Select all that apply Which discharge teaching about doxylamine–pyridoxine (Diclegis) is correct? Select all that apply. - A. Take it on an empty stomach with a glass of water
- B. Crush the tablet if it is hard to swallow
- C. Take it daily, not only when nauseated
- D. Avoid driving until your provider says it is safe
- E. A glass of wine with dinner is fine
Reveal answer & rationale
Common questions
What causes hyperemesis gravidarum?
Is hyperemesis gravidarum just bad morning sickness?
Why thiamine before glucose?
Is Diclegis approved for hyperemesis gravidarum?
Do abnormal thyroid tests in HG need antithyroid medicine?
Will it end by 20 weeks?
Sources
- Hyperemesis Gravidarum — StatPearls — StatPearls (NCBI Bookshelf)
- Wernicke-Korsakoff Syndrome — StatPearls — StatPearls (NCBI Bookshelf)
- Vitamin B1 (Thiamine) Deficiency — StatPearls — StatPearls (NCBI Bookshelf)
- Physiology, Metabolic Alkalosis — StatPearls — StatPearls (NCBI Bookshelf)
- Ondansetron — StatPearls — StatPearls (NCBI Bookshelf)
- DICLEGIS (doxylamine succinate and pyridoxine hydrochloride) — FDA label — U.S. FDA / NLM DailyMed
- Ondansetron tablets (Glenmark) — FDA label — U.S. FDA / NLM DailyMed
- Pregnancy complications — Office on Women's Health — HHS Office on Women's Health
- Nausea and Vomiting — MedlinePlus — National Library of Medicine
- Refeeding Syndrome — StatPearls — StatPearls (NCBI Bookshelf)
Reviewed by Hae Suk Lee, RN
Educational summary for nursing students. Scenarios are fictional teaching cases. Always verify against current guidelines and your institution's protocols before acting in practice. Not medical advice.