What is the appropriate evaluation and management for a reproductive‑age woman presenting with lower pelvic pain?

Evaluation and Management of Lower Pelvic Pain in Reproductive-Age Women

Immediate First Step: Pregnancy Testing

Obtain serum β-hCG immediately in every reproductive-age woman presenting with lower pelvic pain—this single test fundamentally determines your entire diagnostic pathway and imaging strategy. 1, 2, 3

• A positive β-hCG directs you toward pregnancy-related complications (ectopic pregnancy, miscarriage, complications of intrauterine pregnancy), while a negative result shifts focus to non-pregnancy gynecologic or other causes 2, 3
• Critical pitfall: Rare false-negative serum β-hCG tests have been documented in pathology-confirmed ectopic pregnancies, so maintain clinical suspicion even with negative results if imaging shows hemoperitoneum or adnexal mass 4
• The "hook effect" can cause false-negative urine tests in molar pregnancies due to extremely high β-hCG levels overwhelming the assay; if clinical suspicion is high despite negative urine test, obtain serum quantification with dilution 5

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Imaging Algorithm: β-hCG Positive (Pregnancy Confirmed)

Perform combined transvaginal AND transabdominal ultrasound as your first-line imaging—this is the only appropriate initial modality and achieves 99% sensitivity for ectopic pregnancy when β-hCG exceeds 1,500 IU/L. 1, 2, 3

Key Ultrasound Findings and Interpretation:

• Intrauterine gestational sac with yolk sac or fetal pole confirms intrauterine pregnancy 2
• Adnexal mass without intrauterine pregnancy has a positive likelihood ratio of 111 for ectopic pregnancy—this is the single most powerful diagnostic finding 1, 3
• The classic "tubal ring" sign is highly specific for ectopic pregnancy 1, 3
• Absence of adnexal abnormalities on transvaginal ultrasound has a negative likelihood ratio of 0.12, effectively ruling out ectopic pregnancy 1

β-hCG Correlation:

• When β-hCG exceeds 2,000 mIU/mL without visible intrauterine gestational sac, ectopic pregnancy probability rises to approximately 57% 2
• When β-hCG is >3,000 mIU/mL without intrauterine pregnancy, this is strongly suggestive (though not diagnostic) of ectopic pregnancy 1
• Endometrial thickness <8 mm virtually excludes normal intrauterine pregnancy 1
• Endometrial thickness ≥25 mm virtually excludes ectopic pregnancy (present in only 4 cases in one series) 1

When Ultrasound is Inconclusive:

• MRI pelvis without IV contrast is the preferred second-line modality if ultrasound is nondiagnostic or patient cannot tolerate transvaginal approach 1, 6
• MRI demonstrated 95.5% accuracy for cesarean scar pregnancy versus 88.6% for ultrasound 1
• Avoid CT entirely when β-hCG is positive—there is no supporting literature for CT use in this setting, and radiation exposure to a potential viable pregnancy is unacceptable 1, 6
• Gadolinium contrast should be avoided unless absolutely necessary (pregnancy category C) 1, 6

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Imaging Algorithm: β-hCG Negative (Pregnancy Excluded)

Perform combined transvaginal AND transabdominal ultrasound with Doppler as first-line imaging for suspected gynecologic causes. 1, 3

Ultrasound Performance for Gynecologic Pathology:

• 93% sensitivity and 98% specificity for tubo-ovarian abscess 2, 3
• Characteristic findings for tubo-ovarian abscess: thick-walled (>5 mm) complex adnexal mass, "cogwheel" sign, incomplete septations, cul-de-sac fluid 2
• Doppler imaging is mandatory to assess ovarian blood flow for suspected adnexal torsion and to distinguish cystic from solid masses 6, 3
• Adnexal torsion findings: asymmetrically enlarged ovary, twisted pedicle (better seen on multiplanar reformations), decreased or absent Doppler flow, deviation of uterus toward affected side 1

When to Escalate to CT:

Order contrast-enhanced CT of abdomen AND pelvis (never pelvis alone) when: 1, 2

1. Ultrasound findings are equivocal or nondiagnostic 1, 2
2. Clinical suspicion for non-gynecologic pathology is high (appendicitis, bowel obstruction, abscess, urolithiasis) 1, 2
3. Life-threatening condition requires rapid diagnosis 1, 2
4. Severe pain persists or worsens despite negative initial workup 2

• CT demonstrates 89% sensitivity for urgent diagnoses versus 70% for ultrasound alone 3
• CT has 74-95% sensitivity and 80-90% specificity for adnexal torsion 1
• Critical pitfall: Never order CT pelvis alone—it provides insufficient coverage for generalized abdominal pain and must include abdominal imaging 2
• CT identified definitive pathology in 36% of pregnant patients with abdominal pain in retrospective data, including 30% with normal ultrasound who required surgery 2

Role of MRI:

• MRI pelvis (with and without contrast) is first-line when endometriosis is specifically suspected based on clinical presentation, achieving approximately 90.3% sensitivity and 91% specificity 3
• MRI is superior for characterizing adenomyosis due to excellent soft-tissue detail 3
• MRI abdomen and pelvis without contrast is preferred over CT when β-hCG status is uncertain or borderline 2
• For suspected appendicitis in pregnancy, MRI shows 100% sensitivity and 93.6% specificity 2, 6

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Clinical Context and Differential Diagnosis

Most Common Gynecologic Causes by Frequency:

• Ovarian cysts are the most common gynecologic cause of acute pelvic pain in reproductive-age women 3
• Pelvic inflammatory disease (PID) accounts for 20% of acute pelvic pain cases 3
• Endometriosis and adenomyosis are primary causes of chronic or recurrent pelvic pain 3
• Ectopic pregnancy must always be considered until excluded by imaging and β-hCG 1, 2

Key Historical and Physical Exam Findings:

• For suspected PID: Assess sexual history, recent instrumentation, presence of fever, and cervical motion tenderness 6, 3
• For ectopic pregnancy: Most common symptoms are abdominal pain (91%), amenorrhea (76%), irregular bleeding (68%), and adnexal mass (55%) 7
• The classic triad of pain, uterine bleeding, and adnexal mass was present in only 14% of confirmed ectopic pregnancies in one series 7
• Pain characteristics: Distinguish deep pelvic pain from perineal/vulvar/vaginal pain to localize the differential 3
• Red flags: Fever, vaginal bleeding, hemodynamic instability require urgent evaluation 6

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Critical Pitfalls to Avoid

1. Never skip pregnancy testing—failure to obtain β-hCG can result in missed ectopic pregnancy, inappropriate radiation exposure, and maternal mortality 2, 3

2. Never use CT as first-line for gynecologic causes—ultrasound provides equivalent or superior accuracy without radiation 1, 2, 3

3. Never order CT pelvis alone—always combine with abdominal imaging for generalized pain 2

4. Never assume gynecologic origin—15-25% of pelvic pain has gastrointestinal or urologic causes 3

5. Never require multiple criteria before treating suspected PID—initiate empiric broad-spectrum antibiotics immediately when minimum criteria are met (uterine + adnexal + cervical motion tenderness), as requiring additional findings reduces sensitivity and risks permanent reproductive damage 2

6. Never dismiss mild or atypical symptoms—many PID cases present with nonspecific symptoms like abnormal bleeding or dyspareunia 2

7. Never rely solely on urine pregnancy tests—false negatives occur in 1.6% overall and 3.6% in high-risk patients with abdominal pain or vaginal bleeding 8

8. Never use plain radiography—it has no diagnostic role in pelvic pain evaluation 3