What is the initial workup for a patient presenting with uterine cramping?

Initial Workup for Uterine Cramping

The initial workup for uterine cramping should begin with transvaginal ultrasound combined with transabdominal ultrasound and Doppler, as this is the most appropriate first-line imaging modality for suspected gynecologic causes of pelvic pain. 1, 2

Clinical History and Physical Examination

Before imaging, obtain focused clinical information:

• Pregnancy status: Perform urine pregnancy test immediately in all reproductive-age women, as qualitative tests detect hCG at 20-25 mIU/mL 3
• Menstrual history: Last menstrual period, cycle regularity, and relationship of cramping to menses 4
• Pain characteristics: Timing (cyclical vs constant), severity, location, and associated symptoms (bleeding, discharge, fever) 1
• Risk factors: Prior ectopic pregnancy, pelvic inflammatory disease, IUD presence, prior cesarean delivery, or endometriosis 1
• Pelvic examination: Assess for cervical motion tenderness, adnexal masses, peritoneal signs, and bleeding source 1, 5

Laboratory Testing

Quantitative serum β-hCG is essential if pregnancy cannot be excluded, as urine tests may miss very early pregnancies or remain positive weeks after pregnancy termination 3. Serial measurements 48 hours apart provide more diagnostic value than single measurements when pregnancy location is uncertain 3.

Imaging Protocol

Primary Imaging: Combined Ultrasound Approach

Perform both transabdominal and transvaginal ultrasound with Doppler as the initial study 1. This combined approach is superior because:

• Transvaginal ultrasound provides detailed visualization of the uterus, endometrium, adnexa, and cervix 1
• Transabdominal ultrasound captures high-positioned adnexa and free fluid that may be distant from the transvaginal probe 1
• Doppler assessment identifies vascular flow patterns critical for diagnosing conditions like ovarian torsion (absent/abnormal venous flow has 100% sensitivity) and pelvic inflammatory disease 1

Key Ultrasound Findings to Document

In pregnant patients (when β-hCG is positive):

• Presence and location of gestational sac (intrauterine vs extrauterine) 3, 6
• Yolk sac and fetal pole visibility (expected at 5.5 and 6 weeks respectively) 6
• Cardiac activity if gestational age appropriate 6
• Adnexal masses or free fluid suggesting ectopic pregnancy 3
• Critical threshold: At β-hCG ≥3,000 mIU/mL, a gestational sac should be visible; absence suggests ectopic pregnancy requiring immediate consultation 3, 6

In non-pregnant patients:

• Ovarian size, position, and blood flow (torsion shows absent/abnormal venous flow in 100% of cases) 1
• Tubo-ovarian abscess features: thick-walled adnexal mass with internal fluid 1
• Endometrial thickness and characteristics 1
• Free fluid in pelvis (especially echogenic fluid concerning for hemorrhage) 1

Differential Diagnosis Considerations

The ultrasound findings guide diagnosis:

• Ovarian torsion: Enlarged ovary with peripheral follicles, absent venous flow, whirlpool sign (90% confirmed at laparoscopy when present) 1
• Pelvic inflammatory disease: Tubal wall thickness >5 mm, cogwheel sign, hyperemia on Doppler (100% sensitive, 80% specific) 1
• Ectopic pregnancy: Extraovarian adnexal mass without intrauterine pregnancy (positive likelihood ratio 111), free fluid 3
• Primary dysmenorrhea: Normal ultrasound in setting of cyclical pain (affects up to 90% of women) 4

Follow-Up Imaging When Initial Ultrasound Is Inconclusive

If the uterus or adnexa are incompletely visualized on ultrasound, proceed to MRI pelvis without and with contrast 1. MRI is particularly valuable for:

• Characterizing complex adnexal masses 1
• Evaluating suspected adenomyosis or deep endometriosis 1
• Assessing uterine anomalies not fully visualized on ultrasound 1

If a polyp is suspected but not confirmed, sonohysterography is the appropriate next step rather than MRI 1.

Critical Management Pitfalls to Avoid

• Never defer ultrasound based on "low" β-hCG levels in symptomatic patients—22% of ectopic pregnancies occur at levels <1,000 mIU/mL, and rupture can occur at any level 3
• Do not use β-hCG discriminatory thresholds alone (such as 3,000 mIU/mL) to exclude ectopic pregnancy, as this has virtually no diagnostic utility (positive likelihood ratio 0.8) 3
• Obtain immediate gynecology consultation if β-hCG ≥3,000 mIU/mL without visible intrauterine pregnancy (57% ectopic risk) or if peritoneal signs are present 3
• Arrange serial β-hCG measurements every 48 hours when pregnancy location is uncertain, as single measurements have limited diagnostic value 3