How should a 22‑week pregnant woman presenting with isolated vomiting be evaluated and managed?

Management of Isolated Vomiting at 22 Weeks Gestation

At 22 weeks gestation with isolated vomiting, initiate treatment immediately with vitamin B6 (pyridoxine) 10-25 mg every 8 hours combined with doxylamine, and if symptoms persist or worsen, escalate to metoclopramide or ondansetron as second-line therapy. 1, 2

Initial Assessment

Assess severity using the Motherisk Pregnancy-Unique Quantification of Emesis (PUQE) score to guide management: mild (≤6), moderate (7-12), or severe (≥13). 1, 3 This validated scoring system evaluates duration of nausea, number of vomiting episodes, and retching episodes over the past 12 hours. 1

Key clinical features to evaluate:

• Weight trajectory: document current weight and compare to pre-pregnancy weight (≥5% loss indicates hyperemesis gravidarum) 2
• Signs of dehydration: decreased urine output, elevated BUN/creatinine ratio, dry mucous membranes 2
• Ketonuria on urinalysis (though ketonuria alone does not indicate dehydration severity) 4
• Electrolyte panel focusing on potassium and magnesium levels 2
• Liver function tests (40-50% of hyperemesis patients have elevated AST/ALT) 2
• Thyroid function tests if clinical hyperthyroidism suspected 2

At 22 weeks gestation, vomiting is atypical since nausea and vomiting of pregnancy typically peaks at 8-12 weeks and resolves by week 20 in 80% of cases. 1, 2 This late presentation warrants consideration of alternative diagnoses including gallstones, cholecystitis, small bowel obstruction, gastroparesis, or hyperthyroidism. 2 Obtain abdominal ultrasound to rule out hepatobiliary causes. 2

Stepwise Pharmacologic Management

First-Line Therapy

Start with vitamin B6 (pyridoxine) 10-25 mg every 8 hours combined with doxylamine. 1, 2 This combination is FDA-approved and recommended by the American College of Obstetricians and Gynecologists as first-line pharmacologic treatment, safe throughout pregnancy and breastfeeding. 2 Alternative first-line agents include other antihistamines (promethazine, dimenhydrinate) or phenothiazines (prochlorperazine), all with similar safety profiles. 2

Implement dietary modifications simultaneously: small, frequent, bland meals following the BRAT diet (bananas, rice, applesauce, toast), high-protein and low-fat meals, avoiding spicy, fatty, acidic, and fried foods. 1, 3 Identify and avoid specific triggers including foods with strong odors. 1

Second-Line Therapy

If first-line antihistamines fail after 24-48 hours, escalate to metoclopramide 5-10 mg orally every 6-8 hours. 2 Metoclopramide is the preferred second-line agent with less drowsiness, dizziness, and dystonia compared to promethazine in hospitalized patients. 2 Meta-analysis of 33,000 first-trimester exposures shows no increased risk of major congenital defects (OR 1.14,99% CI 0.93-1.38). 2

Ondansetron should be reserved as second-line therapy due to concerns about congenital heart defects when used before 10 weeks gestation, though at 22 weeks this concern is no longer relevant. 2 Both metoclopramide and ondansetron are compatible throughout pregnancy and breastfeeding. 2

Critical caveat: Withdraw metoclopramide or phenothiazines immediately if extrapyramidal symptoms develop. 2 Administer intravenous metoclopramide by slow bolus over at least 3 minutes to minimize extrapyramidal effects. 4

Third-Line Therapy for Severe Refractory Cases

If both ondansetron and metoclopramide fail, reserve methylprednisolone as last resort: 16 mg IV every 8 hours for up to 3 days, then taper over 2 weeks to lowest effective dose, maximum duration 6 weeks. 2 At 22 weeks gestation, the first-trimester concern about cleft palate is no longer applicable. 2

Supportive Care Requirements

Always combine antiemetics with:

• Intravenous fluid resuscitation using normal saline (0.9% NaCl) with additional potassium chloride, guided by daily electrolyte monitoring 2, 4
• Target urine output of at least 1 L/day to ensure adequate hydration 2
• Thiamine supplementation is mandatory: 100 mg daily orally for minimum 7 days, or if unable to tolerate oral intake, switch immediately to IV thiamine 200-300 mg daily 2 This prevents Wernicke's encephalopathy, which can develop after only 20 days of inadequate oral intake. 2
• Electrolyte replacement with particular attention to potassium and magnesium to prevent cardiac arrhythmias 2

Common pitfall to avoid: Do not use PRN or intermittent dosing for moderate-to-severe symptoms. 2 Switch to around-the-clock scheduled antiemetic administration for better symptom control. 2

Monitoring and Escalation Criteria

Monitor daily until stable: body weight and weight trajectory, urine output, electrolytes, renal function, and resolution of ketonuria. 2 Use PUQE score serially to track symptom severity over time. 2

Escalate to hospitalization if:

• Frequent vomiting (≥5-7 episodes daily) despite maximal antiemetics 2
• Progressive weight loss ≥5% of pre-pregnancy weight 2
• Inability to maintain oral intake of 1000 kcal/day for several days 2
• Persistent electrolyte abnormalities despite oral replacement 2

For severe cases requiring hospitalization, consider nasojejunal feeding (better tolerated than nasogastric) before escalating to total parenteral nutrition. 2 Multidisciplinary involvement with maternal-fetal medicine, gastroenterology, and nutrition services is recommended for severe refractory cases. 1, 2