In a 15‑week pregnant woman with isolated lower abdominal pain and no vaginal discharge, what initial evaluation and investigations are indicated?

Initial Evaluation of Hypogastric Pain at 15 Weeks Gestation Without Vaginal Discharge

Begin with transabdominal ultrasound as the primary imaging modality to evaluate for appendicitis, urolithiasis, ovarian torsion, adnexal masses, and other surgical causes of abdominal pain, followed by transvaginal ultrasound if transabdominal imaging is inconclusive, and proceed to non-contrast MRI if ultrasound findings remain equivocal. 1

Primary Diagnostic Considerations

At 15 weeks gestation with isolated lower abdominal pain and no vaginal discharge, the differential diagnosis shifts away from obstetric bleeding complications toward surgical and non-obstetric causes:

• Appendicitis is the most common cause of abdominal pain requiring emergent surgery in pregnant patients 1
• Urolithiasis and urinary tract infection are frequent causes of hypogastric pain in pregnancy 1
• Ovarian torsion or adnexal masses must be excluded 1
• Acute cholecystitis, pancreatitis, or inflammatory bowel disease are less common but important considerations 1
• Placental abnormalities are less likely at this gestational age without vaginal bleeding but should be assessed 1

Initial Clinical Assessment

Critical History Elements

• Pain characteristics: Location (note that appendiceal pain may not follow typical patterns in pregnancy—the appendix migrates superiorly and laterally as the uterus enlarges), onset, radiation, and severity 1
• Associated symptoms: Fever, dysuria, nausea, vomiting, changes in bowel habits 1
• Risk factors: History of kidney stones, gallbladder disease, inflammatory bowel disease 1

Physical Examination Priorities

• Vital signs: Temperature, blood pressure, heart rate to assess for systemic infection or hemodynamic instability 2
• Abdominal examination: Localization of tenderness, peritoneal signs, rebound, guarding 1
• Costovertebral angle tenderness: To assess for pyelonephritis or urolithiasis 1

Laboratory Evaluation

Order the following initial tests:

• Complete blood count with differential: To assess for leukocytosis (though pregnancy normally elevates WBC to 6,000-16,000/μL) 1, 2
• Urinalysis and urine culture: To evaluate for urinary tract infection or urolithiasis 1
• Comprehensive metabolic panel: Including liver function tests and amylase/lipase if upper abdominal involvement 2
• Coagulation panel including fibrinogen: Particularly if any concern for placental complications 2

Imaging Algorithm

Step 1: Transabdominal Ultrasound (First-Line)

Most necessary diagnostic information in pregnant patients with nontraumatic abdominal pain can be obtained with ultrasound as the primary imaging modality. 1

The transabdominal ultrasound should systematically evaluate:

• Appendix visualization: Though challenging, focused right lower quadrant assessment for appendiceal diameter >6mm, non-compressibility, or periappendiceal fluid 1
• Kidneys and ureters: For hydronephrosis, stones, or perinephric fluid collections 1
• Gallbladder: For cholelithiasis, wall thickening, pericholecystic fluid 1
• Adnexa bilaterally: For ovarian masses, torsion (absent Doppler flow), or free fluid 1
• Fetal viability: Confirm fetal cardiac activity 2, 3
• Placental location and appearance: Though placental complications are less likely without bleeding 1

Step 2: Transvaginal Ultrasound (If Transabdominal Inconclusive)

Transvaginal ultrasound is frequently necessary when transabdominal ultrasound is inconclusive or inadequate. 1

Transvaginal imaging provides superior visualization of:

• Adnexal structures: Better assessment for ovarian torsion, masses, or ectopic pregnancy remnants 1
• Cervical length and status: To exclude cervical insufficiency or early labor 1
• Lower uterine segment: For any placental abnormalities or uterine anomalies 1

Step 3: Non-Contrast MRI (If Ultrasound Equivocal)

MRI without contrast is a reliable next step following ultrasound in pregnant patients and avoids the drawbacks of both ultrasound and CT. 1

Non-contrast MRI is particularly valuable for:

• Appendicitis confirmation: When ultrasound is non-diagnostic, MRI has 99% accuracy for acute abdominal pathology 1
• Urolithiasis: Can define level of obstruction and visualize stones as filling defects 1
• Complex adnexal masses: Better tissue characterization than ultrasound 1
• Bowel pathology: Including obstruction, inflammatory bowel disease, or other gastrointestinal causes 1

Critical Pitfalls to Avoid

• Do not assume normal appendix location: In pregnancy, the appendix migrates superiorly and laterally; pain location may not correlate with appendicitis 1
• Do not delay imaging for "observation": Pregnant women are more likely to present with complicated (perforated) appendicitis, and perforation increases fetal loss risk 1
• Do not rely solely on leukocytosis: Pregnancy normally elevates WBC count, making this less specific 1
• Avoid CT as initial imaging: Reserve CT for trauma or when ultrasound and MRI are unavailable or non-diagnostic, as radiation exposure should be minimized 1, 4
• Do not use gadolinium-based MRI contrast routinely: Use only when maternal benefit clearly outweighs potential fetal risks 2

Disposition Based on Findings

Immediate Surgical Consultation Required:

• Confirmed appendicitis on imaging 1
• Ovarian torsion with absent Doppler flow 1
• Acute cholecystitis with complications 1
• Bowel obstruction 1

Urologic Consultation:

• Obstructing urolithiasis with hydronephrosis 1
• Pyelonephritis not responding to antibiotics 1

Obstetric Consultation:

• Any placental abnormalities identified 1
• Cervical insufficiency or preterm labor concerns 1
• Fetal compromise 2

Conservative Management with Close Follow-up:

• Simple urinary tract infection 1
• Non-obstructing kidney stones <5mm 1
• Functional pain with completely normal imaging 1

Special Considerations for Urolithiasis

If urolithiasis is confirmed, ultrasound is the initial imaging modality of choice, with limited intravenous pyelogram (preliminary film plus 15-minute and 60-minute post-contrast films) considered only if ultrasound is unrevealing and symptoms are severe. 1 Ureteroscopic stone removal is safe and effective in pregnancy, with superior outcomes compared to temporizing measures like stenting, which require multiple exchanges due to rapid encrustation. 1