How should a healthy 26‑week pregnant woman with lower abdominal pain and no vaginal bleeding be evaluated and managed?

Evaluation and Management of Lower Abdominal Pain at 26 Weeks Without Bleeding

Perform transabdominal ultrasound immediately as the first-line diagnostic study to evaluate for placental abruption, preterm labor, uterine rupture, appendicitis, urolithiasis, and ovarian torsion—even without vaginal bleeding, placental abruption can present with pain alone and predicts worse perinatal outcomes. 1

Initial Imaging Approach

Begin with transabdominal ultrasound as it provides the majority of diagnostic information needed for painful presentations in the second and third trimesters. 2 This study must comprehensively assess:

• Placental location and integrity: Look for retroplacental clot or areas of placental separation, as abruption frequently presents without bleeding 1
• Myometrial continuity: Measure lower uterine segment thickness; <2.5 mm predicts uterine dehiscence, especially in patients with prior cesarean delivery 2
• Cervical assessment: Evaluate from external to internal os for signs of preterm labor 2
• Appendix visualization: Diameter >6 mm, lack of compressibility, or peri-appendiceal fluid indicate appendicitis 1
• Renal evaluation: Identify hydronephrosis or echogenic stones 1
• Adnexal structures: Assess for masses or absent Doppler flow suggesting torsion 1

When to Upgrade to Transvaginal Ultrasound

Proceed to transvaginal ultrasound when transabdominal imaging is inadequate or inconclusive, as it provides superior visualization of critical structures. 2 Specific indications include:

• Precise cervical length measurement: <25 mm with pain markedly increases preterm delivery risk and mandates obstetric involvement 1
• Lower uterine segment evaluation: Better assessment of isthmus integrity and thickness to rule out rupture 2
• Placental margin detail: Accurate measurement of distance from leading edge to internal os 2
• Detection of intrauterine clot: Identify areas contiguous with placenta that lack blood flow on color Doppler, suggesting acute abruption 2

Role of Doppler Ultrasound

Add color or power Doppler imaging to identify placental abruption, as acute clots have echogenicity similar to placenta and can be difficult to diagnose without Doppler confirmation. 2 An area of interest contiguous with the placenta showing no blood flow suggests acute clot from placental separation. 2

When MRI Is Indicated

Order non-contrast MRI when ultrasound remains nondiagnostic, as it provides approximately 99% accuracy for acute abdominal pathology while avoiding ionizing radiation. 1

Conditions Requiring Immediate Obstetric Consultation

• Placental abruption identified on ultrasound (even pain-only presentation): Prepare for possible delivery 1
• Cervical length <25 mm with pain: Consider antenatal corticosteroids 1
• Myometrial disruption or lower uterine segment <2.5 mm: Prepare for possible surgical intervention 1
• Regular painful contractions with cervical change: Initiate tocolysis if appropriate 1

Conditions Requiring Urgent Surgical Consultation

• Appendicitis (ultrasound criteria met): Operative management as indicated 1
• Ovarian torsion (absent Doppler flow): Prompt detorsion required 1
• Acute cholecystitis with complications: Consider cholecystectomy 1
• Bowel obstruction on imaging: Evaluate need for operative decompression 1

Conditions Requiring Urologic Referral

• Obstructing stone with hydronephrosis: Ureteroscopic stone removal preferred over temporary stenting 1
• Pyelonephritis unresponsive to antibiotics: Consider escalation or drainage 1

Critical Pitfalls to Avoid

Do not dismiss pain without bleeding—placental abruption may present solely with pain, and ultrasound confirmation of abruption predicts poorer perinatal outcomes even in the absence of vaginal bleeding. 1

Do not delay imaging—postponing diagnosis of appendicitis increases the chance of perforation and fetal loss. 1

Do not rely on classic appendix location—the appendix migrates upward and laterally during pregnancy, masking typical right-lower-quadrant tenderness. 1

Do not interpret leukocytosis in isolation—pregnancy-related leukocytosis (6,000–16,000/µL) reduces its specificity for infection. 1

Do not use CT as the initial study—reserve it for trauma or when both ultrasound and MRI are unavailable. 1

Do not overfill the bladder during transabdominal scanning, as this can compromise visualization of the lower uterine segment and cervix. 2