How to manage nausea and vomiting in the 3rd trimester of pregnancy?

Management of Nausea and Vomiting in the Third Trimester

Start with dietary modifications and vitamin B6, then escalate to doxylamine-pyridoxine combination, followed by metoclopramide or promethazine for persistent symptoms, reserving ondansetron and corticosteroids for severe refractory cases requiring hospitalization. 1, 2

Assessment of Severity

• Use the PUQE (Pregnancy-Unique Quantification of Emesis) score to quantify severity: mild (≤6), moderate (7-12), or severe (≥13) 1
• Evaluate for hyperemesis gravidarum if there is intractable vomiting, dehydration, weight loss >5% of prepregnancy weight, and electrolyte imbalances 1
• Check electrolytes, liver enzymes (elevated in 40-50% of hyperemesis cases), and assess for ketonuria 2, 3
• Rule out other causes of nausea and vomiting unrelated to pregnancy 4, 5

First-Line Treatment (Mild Symptoms, PUQE ≤6)

• Implement dietary modifications: small, frequent, bland meals (BRAT diet), high-protein and low-fat foods, avoiding spicy, fatty, acidic, and fried foods 1
• Add vitamin B6 (pyridoxine) 10-25 mg every 8 hours 1, 2
• Consider ginger 250 mg capsules four times daily 1

Second-Line Treatment (Moderate Symptoms, PUQE 7-12)

• Prescribe doxylamine-pyridoxine combination (Diclectin: 10 mg doxylamine/10 mg pyridoxine) as the preferred first-line pharmacologic therapy 2
• Alternative H1-receptor antagonists if doxylamine unavailable: promethazine or dimenhydrinate 1, 2
• Promethazine is safe throughout pregnancy with extensive clinical experience and should be used when vitamin B6 and doxylamine are insufficient 2

Third-Line Treatment (Severe Symptoms, PUQE ≥13)

• Metoclopramide 5-10 mg orally every 6-8 hours is the preferred third-line agent with no significant increase in major congenital defects (odds ratio 1.14,99% CI 0.93-1.38 in 33,000 first-trimester exposures) 2
• Metoclopramide has similar efficacy to promethazine but with fewer side effects including less drowsiness, dizziness, and dystonia 2
• Ondansetron can be used as a second-line agent, but at 20+ weeks gestation the safety concerns are minimal compared to early pregnancy 2
  • In early pregnancy (<10 weeks), ondansetron carries a marginal absolute risk increase of 0.03% for cleft palate and 0.3% for ventricular septal defects 2
  • By the third trimester, these organogenesis-related risks are no longer relevant 2

Hospitalization and IV Management (Severe/Refractory Cases)

• Admit for IV hydration with normal saline (0.9% NaCl) plus potassium chloride guided by daily electrolyte monitoring 2
• Always provide thiamine supplementation (100 mg IV for minimum 7 days, then 50 mg daily maintenance) before any dextrose administration to prevent Wernicke encephalopathy 2, 3
• IV metoclopramide 10 mg administered slowly over 1-2 minutes every 6-8 hours is the preferred IV antiemetic 2
• IV ondansetron 0.15 mg/kg per dose (maximum 16 mg) infused over 15 minutes can be used when metoclopramide is ineffective 2, 6

Last Resort Therapy (Severe Refractory Hyperemesis)

• Methylprednisolone 16 mg IV every 8 hours for up to 3 days, then taper over 2 weeks to the lowest effective dose, limiting maximum duration to 6 weeks 2
• At 20+ weeks gestation, corticosteroid use is safer as the risk of cleft palate (relevant before 10 weeks) is no longer a concern 2
• Methylprednisolone reduces rehospitalization rates in severe cases 2

Critical Clinical Pearls

• Early intervention is crucial to prevent progression to hyperemesis gravidarum—don't delay pharmacologic treatment waiting for dietary modifications alone 2, 4, 5
• While nausea and vomiting typically peaks at 8-12 weeks and subsides by week 20, persistent symptoms in the third trimester warrant aggressive treatment 1, 2
• Monitor for signs of dehydration: orthostatic hypotension, decreased skin turgor, dry mucous membranes 2
• Withdraw metoclopramide if extrapyramidal symptoms develop 2
• Consider enteral or parenteral nutrition if weight loss persists despite pharmacotherapy 2
• Coordinate care with maternal-fetal medicine specialists for refractory cases 1