What is the appropriate workup for an 18-week pregnant 30-year-old female presenting to the emergency department (ED) with lower back pain?

Workup for Lower Back Pain in an 18-Week Pregnant 30-Year-Old Female in the Emergency Department

The initial workup for a pregnant woman with lower back pain in the emergency department should focus on ruling out serious underlying conditions through targeted history, physical examination, and appropriate imaging, with ultrasound as the first-line imaging modality if imaging is indicated.

Initial Assessment

History - Key Elements to Assess

• Onset, duration, location, and quality of pain
• Radiation of pain (lumbar vs. pelvic girdle pain)
• Aggravating and relieving factors
• Associated symptoms:
  • Urinary symptoms (urgency, frequency, dysuria)
  • Neurological symptoms (numbness, weakness, saddle anesthesia)
  • Fever or chills
  • Vaginal bleeding or discharge
• Previous history of back pain (especially during pregnancy)
• Occupational factors (heavy lifting, prolonged standing) 1

Physical Examination

• Vital signs (temperature, blood pressure, heart rate)
• Abdominal examination
• Back examination:
  • Point tenderness
  • Range of motion
  • Pelvic pain provocation tests to differentiate pelvic girdle pain from lumbar pain 2
• Neurological examination:
  • Motor strength in lower extremities
  • Sensory testing
  • Deep tendon reflexes
  • Straight leg raise test
• Obstetric examination:
  • Fundal height
  • Fetal heart tones

Laboratory Testing

• Complete blood count (to assess for infection)
• Urinalysis and urine culture (to rule out urinary tract infection)
• C-reactive protein or ESR (if infection or inflammation suspected)

Imaging Considerations

When to Consider Imaging

Imaging should be considered if there are "red flags" suggesting serious underlying pathology 1:

• Severe or progressive neurological deficits
• Suspected cauda equina syndrome
• Fever or other signs of infection
• History of cancer
• Trauma
• Unexplained weight loss
• Failure to improve with conservative management

Imaging Algorithm

1. Ultrasound (First-line) 1

   • Safest option during pregnancy
   • Can evaluate for appendicitis, kidney stones, or other non-spine causes of pain
   • Limited utility for evaluating the spine itself

2. MRI Without Contrast (Second-line) 1

   • If neurological deficits are present or cauda equina syndrome is suspected
   • No radiation exposure to fetus
   • Can evaluate soft tissue pathology, assess vertebral marrow, and spinal canal patency

3. CT or X-ray (Last resort) 1

   • Only if absolutely necessary and benefits outweigh risks
   • Consider low-dose CT techniques if MRI is contraindicated or unavailable

Differential Diagnosis to Consider

• Pregnancy-related musculoskeletal pain (most common) 1, 3
• Lumbar disc herniation
• Pelvic girdle pain 2
• Urinary tract infection
• Kidney stones
• Appendicitis (especially with right-sided pain) 1
• Preterm labor
• Placental abruption (with associated vaginal bleeding)
• Rare but serious: malignancy, infection, or cauda equina syndrome 4

Important Considerations

• Back pain affects approximately 50% of pregnant women 5
• Combined lumbar and pelvic girdle pain has a worse prognosis than either condition alone 2
• Occupation and previous history of back pain are significant risk factors 1, 6
• Pregnancy-related back pain can significantly impact quality of life and daily activities 6

Red Flags Requiring Urgent Evaluation

• Urinary retention or incontinence (possible cauda equina syndrome)
• Saddle anesthesia
• Bilateral leg weakness or numbness
• Fever with back pain (possible infection)
• Severe, unrelenting pain unrelated to movement
• History of cancer with new back pain 4

Remember that while back pain is common in pregnancy, serious underlying conditions must be ruled out before attributing symptoms to normal pregnancy changes. The workup should balance the need for diagnostic certainty with minimizing radiation exposure to the fetus.