Thiamine (Vitamin B1)
Thiamine supplementation (vitamin B1) must be given to all pregnant women with hyperemesis gravidarum and prolonged vomiting, administered as either oral 100 mg three times daily or intravenous vitamin B complex (Pabrinex®), and critically, this must be given before any dextrose or parenteral nutrition administration. 1
Critical Rationale: Preventing Wernicke Encephalopathy
The absolute priority for vitamin supplementation in hyperemesis gravidarum is thiamine to prevent Wernicke encephalopathy, a potentially fatal neurological emergency that carries devastating consequences:
- Maternal mortality: 5%
- Pregnancy loss: 50%
- Chronic cognitive disorders: 65.4% 1
The Dextrose-Thiamine Sequence is Life-Saving
A critical pitfall that has caused maternal deaths: administering intravenous dextrose or parenteral nutrition before thiamine supplementation can precipitate Wernicke encephalopathy 1, 2. The carbohydrate load depletes remaining thiamine stores, triggering this neurological catastrophe. Two case reports document pregnant women with hyperemesis who developed confusion, diplopia, unsteadiness, and seizures after inadvertent carbohydrate administration without thiamine 3.
Dosing Algorithm
For all admitted patients with vomiting or severely reduced dietary intake:
- Oral route: Thiamine 100 mg three times daily
- Intravenous route: Vitamin B complex (Pabrinex®) as part of IV therapy
- Timing: Before any dextrose-containing fluids or parenteral nutrition 1
Additional Vitamin Considerations
Pyridoxine (Vitamin B6)
While not the primary vitamin for preventing serious complications, pyridoxine (vitamin B6) combined with doxylamine is a first-line antiemetic treatment with Grade A evidence for safety and efficacy 1. Meta-analysis demonstrates significant improvement in nausea symptoms with pyridoxine supplementation 4.
Vitamin K
Women with history of gastric reduction surgery require special attention as they have increased risk of vitamin K deficiency in addition to thiamine 1.
Iron Supplementation Caveat
Consider discontinuing or switching route of iron supplements if they exacerbate symptoms—two-thirds of women with nausea and vomiting reported improvement after stopping oral iron 1.
Clinical Recognition of Thiamine Deficiency
Wernicke encephalopathy in hyperemesis gravidarum presents with:
- Blurred vision
- Unsteadiness
- Confusion, memory problems, or drowsiness
- Nystagmus, ophthalmoplegia
- Hyporeflexia or areflexia
- Gait and/or finger-nose ataxia
The presentation tends to be episodic and of slow onset in pregnancy, making it easy to miss 1.
Evidence Strength
This recommendation comes from the 2024 Royal College of Obstetricians and Gynaecologists Green-top Guideline No. 69, endorsed by multiple Royal Colleges and professional societies 1. While graded as Grade D evidence due to the nature of available studies, the recommendation is unequivocal given the catastrophic consequences of thiamine deficiency and the preventable nature of Wernicke encephalopathy in this setting.