How should a 26‑week pregnant woman presenting with acute sharp abdominal pain be evaluated and managed?

Evaluation and Management of Sharp Abdominal Pain at 26 Weeks Gestation

Begin with ultrasound as the primary imaging modality, followed by MRI without contrast if ultrasound is inconclusive, and reserve CT only for life-threatening situations when other imaging cannot establish a diagnosis. 1

Immediate Assessment Priorities

Evaluate for life-threatening conditions first:

• Check hemodynamic status (blood pressure, heart rate) - tachycardia is a significant predictor of serious complications 2
• Assess for peritoneal signs (guarding, rebound tenderness, rigidity) 3, 2
• Monitor fetal heart rate continuously 4
• Document presence or absence of vaginal bleeding 2
• Obtain vital signs including temperature - fever with abdominal pain suggests infection requiring prompt evaluation 2

Critical Differential Diagnoses at 26 Weeks

Most Common Non-Obstetric Surgical Emergency

Appendicitis is the most common cause of abdominal pain requiring emergency surgery in pregnant patients. 1, 2, 4 At 26 weeks, the appendix is displaced superiorly and laterally by the gravid uterus, making clinical presentation atypical 4. Pain may localize to the right upper quadrant or flank rather than McBurney's point 1.

Other Critical Diagnoses to Exclude

• Urolithiasis/pyelonephritis - renal colic is the most common non-obstetric cause of abdominal pain requiring hospitalization in pregnancy 1
• Ovarian torsion - can cause acute severe pain with enlarged ovary and decreased Doppler flow on ultrasound 4
• Cholecystitis - pregnancy increases gallstone formation risk 4
• Placental abruption - though ultrasound sensitivity is only 40-50% 4
• Spontaneous uterine vein rupture - rare but life-threatening cause of acute abdomen with hemoperitoneum 5
• Bowel obstruction or perforation 1

Diagnostic Algorithm

Step 1: Initial Laboratory Studies

• Complete blood count 2
• Urinalysis 2
• Liver function tests if right upper quadrant pain 3
• Coagulation profile if bleeding suspected 4

Step 2: Imaging Strategy

Primary imaging: Transabdominal ultrasound 1, 2

• Evaluate for free fluid, appendix visualization, ovarian pathology, gallbladder abnormalities 4
• Assess fetal well-being and placental position 4
• Check for hydronephrosis or urolithiasis 1

If ultrasound is inconclusive: MRI abdomen/pelvis without IV contrast 1

• MRI has 97% sensitivity and 95% specificity for diagnosing appendicitis in pregnancy 2, 4
• Appendix nonvisualization rate on MRI is 30.9%, lower than ultrasound 1
• If the appendix is not visualized but no ancillary signs of appendicitis are present on quality MRI, this indicates low risk for appendicitis 1
• The T1 bright appendix sign (high-intensity signal filling >50% of appendix length) has 95.5% specificity for normal appendix 1
• MRI can diagnose urolithiasis via static-fluid MR urography without gadolinium 1

Reserve CT with IV contrast for life-threatening situations only 2

• Use only when diagnosis cannot be made by ultrasound or MRI and immediate intervention is needed 2
• Single-acquisition CT delivers <25 mGy, posing minimal fetal risk 2
• Do not withhold CT in truly life-threatening situations 1

Management Principles

When Surgical Pathology is Identified

Do not delay surgical intervention when appendicitis, ovarian torsion, or cholecystitis is diagnosed - maternal and fetal outcomes worsen with delayed treatment. 2

• Laparoscopic surgery is safe in the second trimester and preferred over open surgery when feasible 2
• Position patient in left lateral tilt during procedures to avoid aortic/IVC compression by gravid uterus 2
• If ureteroscopy is needed for ureteral stones, holmium laser has minimal tissue penetration, limiting theoretical fetal injury risk 1

Conservative Management Considerations

Do not attribute all abdominal pain to normal pregnancy changes without excluding serious pathology first. 2

• Serial abdominal examinations every 4-6 hours to detect peritoneal signs, increasing pain, or guarding 3
• Continuous fetal heart rate monitoring 4
• IV hydration for volume depletion if indicated 3
• Antiemetics for symptom control if needed 3

Disposition Criteria

Admit for observation if: 2

• Unable to tolerate oral intake
• Persistent vomiting
• Significant pain requiring IV analgesia
• Peritoneal signs present
• Hemodynamic instability

Discharge with 24-48 hour follow-up if: 2

• Tolerating oral intake
• Pain controlled with oral analgesia
• Vital signs stable
• No peritoneal signs
• Reliable follow-up arranged

Critical Pitfalls to Avoid

• Do not rely on normal ultrasound alone to exclude placental abruption - sensitivity is only 40-50% 4
• Do not delay imaging due to radiation concerns - MRI provides excellent diagnostic accuracy without radiation exposure 1
• Do not assume pain location follows typical patterns - anatomical displacement by gravid uterus alters presentation 2
• Do not wait for fever or leukocytosis - these may be absent or difficult to interpret in pregnancy 6
• Repeat imaging has low yield if initial comprehensive imaging was negative and clinical status is stable, but consider repeat ultrasound or CT if clinical deterioration occurs 3