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, reserving CT only for life-threatening situations when other modalities fail to establish a diagnosis. 1, 2

Initial Clinical Assessment

Immediately assess vital signs with particular attention to fever, tachycardia, and tachypnea, as this triad indicates serious complications requiring urgent intervention. 2 Tachycardia is a significant predictor of serious complications in pregnant patients and should never be dismissed as physiologic. 2

Critical Laboratory Studies

• Obtain complete blood count with differential to assess for leukocytosis suggesting infection or inflammation 2
• Perform urinalysis with culture to evaluate for urinary tract infection or urolithiasis 2
• Check comprehensive metabolic panel to assess renal function and electrolytes 3
• Confirm β-hCG level if early pregnancy status is uncertain 2

Pain Characterization

• Document exact location, radiation pattern, severity, timing, and associated symptoms (nausea, vomiting, fever, vaginal bleeding) to guide differential diagnosis 2
• Note that at 26 weeks gestation, the gravid uterus displaces abdominal organs upward, so appendicitis may present with higher right-sided pain than typical McBurney's point 1

Differential Diagnosis Priority

Most Critical Diagnoses to Exclude

Appendicitis is the most common non-obstetric surgical emergency in pregnancy and occurs most frequently in early to mid-pregnancy. 1 Pregnant women are more likely to present with perforated appendicitis, and perforation carries higher risk of fetal loss, making early diagnosis critical. 1

• Urolithiasis/pyelonephritis: Physiologic hydronephrosis occurs in >80% of pregnancies after 20 weeks, more commonly on the right side, complicating diagnosis 3
• Cholecystitis: Most common surgical cause of upper abdominal pain in pregnancy 4
• Ovarian torsion: Can cause acute severe pain requiring urgent surgical intervention 2
• Placental abruption or preterm labor: Must be evaluated by obstetrics if any vaginal bleeding or contractions present 2

Imaging Algorithm

First-Line: Ultrasound

Ultrasound abdomen is the mandatory initial imaging study because it provides diagnostic information without radiation exposure and can identify most life-threatening conditions. 1, 2, 4

• For right lower quadrant pain: focused appendiceal ultrasound has 90% sensitivity and 95% specificity when performed by experienced operators 1
• For flank pain: renal ultrasound identifies hydronephrosis in 84% of pregnant women with acute flank pain 3
• For upper abdominal pain: highly sensitive for cholecystitis, cholelithiasis, and hepatobiliary pathology 4

Second-Line: MRI Without Contrast

If ultrasound is nondiagnostic or equivocal, proceed immediately to MRI abdomen/pelvis without IV contrast. 1, 2, 4 This is the preferred next step across all guidelines.

• MRI demonstrates 96.8% sensitivity and 99.2% specificity for appendicitis in pregnant women 1
• MRI achieves 99% accuracy for diagnosing acute abdominal conditions including bowel inflammation, obstruction, and pancreaticobiliary disease 4
• MRI can detect ureteral calculi with approximately 69% sensitivity for exact stone location 3
• The combination of ultrasound followed by MRI is the most commonly used imaging strategy (41% of cases) in pregnant women with suspected appendicitis 1

Third-Line: CT (Reserved for Emergencies Only)

CT should only be used when both ultrasound and MRI are nondiagnostic or unavailable AND clinical suspicion remains high for a life-threatening condition. 1, 2, 4

• Low-dose CT without IV contrast delivers approximately 705 mrad fetal dose (<25 mGy), which poses minimal fetal risk 2, 3
• CT with IV contrast may be necessary for suspected mesenteric ischemia, internal hernia, or bowel perforation when immediate intervention is needed 1, 2
• Do not withhold CT in truly life-threatening situations, as maternal death poses greater fetal risk than radiation exposure 1

Management Based on Diagnosis

If Appendicitis Confirmed

• Immediate surgical consultation is mandatory 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 the gravid uterus 2
• Do not delay surgical intervention, as maternal and fetal outcomes worsen with delayed treatment 2

If Urolithiasis Without Infection

• Conservative management succeeds in 70-80% of cases: adequate hydration, rest, acetaminophen for analgesia (avoid NSAIDs after 20 weeks), antiemetics as needed 3
• Proceed to urologic intervention if: pain refractory to conservative therapy after 48-72 hours, fever/leukocytosis develops, significant obstruction with declining renal function, or persistent preterm labor signs 3
• Retrograde ureteral stenting is preferred over percutaneous nephrostomy 3

If Infection Present

• Urgent urinary decompression within 24 hours is mandatory if fever or leukocytosis develops to prevent urosepsis and preterm labor 3
• Immediate surgical intervention for any intra-abdominal abscess or peritonitis 2

If Cholecystitis Confirmed

• Surgical consultation for possible cholecystectomy, which can be performed laparoscopically in second trimester 2

Critical Pitfalls to Avoid

• Never attribute all abdominal pain to "normal pregnancy changes" without excluding serious pathology first 2
• Do not delay imaging due to radiation concerns when ultrasound and MRI are available as safe alternatives 1, 2
• Recognize that leukocytosis up to 15,000-16,000/μL can be physiologic in pregnancy, but values above this or with left shift suggest pathology 2
• Do not delay surgical intervention once a surgical diagnosis is established, as perforation rates and complications increase dramatically with delays beyond 48 hours 2

Disposition Criteria

Discharge is appropriate only if: patient tolerates oral intake, pain is controlled with oral analgesia, vital signs are stable, no peritoneal signs present, and reliable 24-48 hour follow-up is arranged. 2 Otherwise, admit for observation and further evaluation.