How is appendicitis triaged in pregnant women across different trimesters?

Triaging Appendicitis in Pregnancy Across Trimesters

Ultrasound should be used as the first-line imaging modality for suspected appendicitis in pregnant women, followed by MRI if ultrasound is inconclusive, regardless of trimester. 1, 2

Diagnostic Approach by Trimester

Initial Assessment (All Trimesters)

• Suspect appendicitis in any pregnant woman with new-onset abdominal pain
• Key clinical features:
  • Migration of periumbilical/diffuse pain to right lower quadrant
  • Presence of uterine contractions (significantly associated with appendicitis)
  • Note: Fever and leukocytosis are unreliable diagnostic indicators in pregnancy 2

First Trimester

• Imaging Protocol:
  • Transabdominal ultrasound as first-line imaging
  • Appendix visualization rate: ~34% (higher than later trimesters)
  • If ultrasound inconclusive → proceed to MRI without contrast
• Risk Considerations:
  • Highest risk of spontaneous abortion following appendectomy (33%) 3
  • Lower anatomical distortion compared to later trimesters

Second Trimester

• Imaging Protocol:
  • Transabdominal ultrasound as first-line imaging
  • If ultrasound inconclusive (common) → MRI without contrast
  • MRI sensitivity: 91-100%, specificity: 93-98% 1
• Risk Considerations:
  • Risk of premature delivery: ~14% following appendectomy 3
  • Represents highest incidence of appendicitis during pregnancy

Third Trimester

• Imaging Protocol:
  • Transabdominal ultrasound as first-line imaging (limited utility)
  • MRI without contrast when ultrasound inconclusive
  • Highest rate of appendix non-visualization on MRI (up to 43%) due to gravid uterus 1
• Risk Considerations:
  • Anatomical displacement of appendix (may be located in right upper quadrant)
  • Lower risk of pregnancy complications following appendectomy compared to earlier trimesters 3

Imaging Considerations

Ultrasound Performance

• Sensitivity: 12.5-61.2%, Specificity: 80-99.2% 1
• Limitations:
  • High non-visualization rates (34-71%) 1
  • Accuracy decreases beyond first trimester 1
  • False-negative rate: up to 8% 1

MRI Performance

• Sensitivity: 89-100%, Specificity: 93.6-99.2% 1
• Benefits:
  • Can identify alternative diagnoses in 10-43% of cases 1
  • High negative predictive value (96-100%) 1
  • No radiation exposure
• Interpretation when appendix not visualized:
  • If no ancillary signs of inflammation → report as "low risk for appendicitis" rather than "indeterminate" 1
  • T1 bright appendix sign (high-intensity signal filling >50% of appendix length) is specific for normal appendix 1

Management Decisions

Timing of Intervention

• Prompt surgical intervention within 24 hours of symptom onset is critical
• Delay beyond 20 hours significantly increases perforation risk 4
• Perforation rates in pregnancy are higher than in non-pregnant patients 2

Surgical Approach

• Laparoscopic appendectomy is preferred over open approach 2
• Timing of surgery should not be delayed for completion of antibiotic courses
• Prophylactic antibiotics recommended for all suspected appendicitis cases during pregnancy 3

Pitfalls to Avoid

1. Attributing symptoms to normal pregnancy - right lower quadrant pain warrants thorough evaluation 2
2. Delaying imaging - increases risk of perforation and worsens maternal/fetal outcomes 2, 5
3. Relying on traditional inflammatory markers - fever and leukocytosis are unreliable in pregnancy 2
4. Prolonged observation - observation period should not exceed 20 hours from symptom onset 4
5. Dismissing MRI with non-visualized appendix - absence of secondary inflammatory signs still has high NPV 1

By following this trimester-specific approach to imaging and maintaining a low threshold for surgical intervention, maternal morbidity and fetal loss can be minimized in pregnant women with suspected appendicitis.