What is the most appropriate next step in management for a pregnant patient at 33 weeks of gestation with fever, rigors, loin pain, and a history of urinary tract infections (UTIs)?

Management of Suspected Pyelonephritis in Pregnancy at 33 Weeks

The most appropriate next step is septic screening (Option C), followed by immediate initiation of intravenous antibiotics while awaiting culture results. This patient presents with classic signs of acute pyelonephritis in pregnancy—fever, rigors, and loin pain—which constitutes a medical emergency requiring urgent assessment for sepsis and prompt antimicrobial therapy 1, 2.

Immediate Management Priorities

Septic screening must be performed immediately because pregnant patients with pyelonephritis are at high risk for progression to urosepsis, which threatens both maternal and fetal outcomes 1, 2. The septic screen should include:

• Blood cultures (before antibiotics) to identify bacteremia 1
• Complete blood count to assess for leukocytosis and evaluate severity 3
• Serum creatinine and renal function tests to detect acute kidney injury 3
• C-reactive protein to gauge inflammatory response 3
• Urine culture with antimicrobial susceptibility testing, which is mandatory in all cases of suspected pyelonephritis 1, 2
• Urinalysis to confirm pyuria and bacteriuria 1, 2

Why Imaging Is NOT the First Priority

Initial imaging is not indicated for uncomplicated acute pyelonephritis, even in pregnancy 1, 2. The American College of Radiology and European Urology guidelines are clear that imaging should only be performed if:

• The patient remains febrile after 72 hours of appropriate antibiotic therapy 1, 2
• Clinical deterioration occurs despite treatment 1, 2
• There is suspicion of complications such as obstruction, abscess, or emphysematous pyelonephritis 1

Ultrasound (Option D) would be appropriate later if fever persists beyond 72 hours or if there is concern for obstruction given her history of recurrent UTIs 3, 4. While physiologic hydronephrosis is common after 20 weeks gestation due to uterine compression, ultrasound can safely evaluate for pathologic obstruction, stones, or abscess without radiation exposure 3.

MRI pelvis (Option A) and ureteroscopy (Option B) are not appropriate initial steps in this acute presentation. These would only be considered for specific complications identified after initial management and imaging 3.

Antibiotic Therapy

Immediate intravenous antibiotics must be started after obtaining cultures 1, 5. For pregnant patients with pyelonephritis, hospitalization with IV therapy is indicated 5. Appropriate empiric regimens include:

• Ceftriaxone 1-2g IV daily (preferred first-line agent) 1
• Cefepime 1-2g IV every 8-12 hours (alternative) 6
• Treatment duration is typically 7-14 days 1

Critical Pitfalls to Avoid

Do not delay antibiotic therapy while waiting for imaging results 1, 2. The priority sequence is: septic screening → immediate antibiotics → clinical monitoring → imaging only if indicated by treatment failure 1, 2.

Do not assume hydronephrosis seen on ultrasound is purely physiologic in a febrile pregnant patient with recurrent UTI history, as obstructive pyelonephritis can rapidly progress to urosepsis 3.

Monitor closely for preterm labor, as pyelonephritis is a significant risk factor for premature delivery 3. The risk resolves once the infection is adequately treated 3.

Expected Clinical Course

95% of patients with uncomplicated pyelonephritis become afebrile within 48 hours, and nearly 100% within 72 hours of appropriate therapy 1. If this patient remains febrile beyond 72 hours despite appropriate antibiotics, then proceed with renal ultrasound to evaluate for complications such as obstruction, abscess formation, or stones 1, 2, 4.

Given her history of two prior UTIs during this pregnancy, she is at higher risk for complications and may require urologic evaluation postpartum 3.