What is the recommended antibiotic regimen for an uncomplicated urinary tract infection in a pregnant woman, taking into account gestational age and contraindications such as glucose‑6‑phosphate dehydrogenase deficiency?

Urinary Tract Infection in Pregnancy: Antibiotic Management

For uncomplicated UTI in pregnancy, treat asymptomatic bacteriuria and symptomatic cystitis with fosfomycin trometamol 3g single dose, nitrofurantoin 100mg twice daily for 5-7 days, or amoxicillin/cephalosporins based on susceptibility, avoiding trimethoprim in the first trimester and sulfonamides in the third trimester. 1, 2, 3

Screening and Diagnosis

• All pregnant women require screening for asymptomatic bacteriuria (ASB) with urine culture in the first trimester, as ASB affects 2-7% of pregnancies and increases risk of pyelonephritis, preterm labor, and low birth weight 1, 3
• Urine culture is mandatory for pregnant women presenting with any urinary symptoms, unlike non-pregnant women where empiric treatment is acceptable 1
• Dipstick testing alone is insufficient for diagnosis in pregnancy; culture and susceptibility testing guide appropriate therapy 1, 3

First-Line Treatment Options for Uncomplicated Cystitis and Asymptomatic Bacteriuria

Preferred Agents:

• Fosfomycin trometamol 3g single dose - safe, effective, and convenient for both ASB and acute cystitis 1, 2, 3
• Nitrofurantoin 100mg twice daily for 5-7 days - avoid near term (after 36 weeks) due to theoretical risk of neonatal hemolysis 1, 3
• Amoxicillin 500mg three times daily for 3-7 days if organism is susceptible (cure rates ~80%) 4, 5, 3
• Cephalosporins (e.g., cefadroxil 500mg twice daily for 3-7 days) - safe throughout pregnancy 1, 5, 3

Critical Contraindications by Trimester:

• Trimethoprim: contraindicated in first trimester due to folate antagonism and neural tube defect risk 1
• Sulfonamides (including trimethoprim-sulfamethoxazole): contraindicated in third trimester due to risk of neonatal kernicterus 1
• Fluoroquinolones: avoid throughout pregnancy due to concerns about cartilage development, though they remain standard for pyelonephritis in non-pregnant women 1, 3

Special Consideration: Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency

• Nitrofurantoin is absolutely contraindicated in patients with G6PD deficiency due to risk of severe hemolytic anemia 3
• Sulfonamides are also contraindicated in G6PD deficiency for the same reason 3
• In G6PD-deficient pregnant patients, use fosfomycin trometamol, amoxicillin, or cephalosporins as first-line options 1, 3

Treatment Duration and Follow-Up

• Short-course therapy (single dose fosfomycin or 3-5 day courses) is preferred over 7-10 day regimens for uncomplicated lower UTI in pregnancy 1, 4
• Repeat urine culture 7 days after completing therapy is mandatory to document cure, as recurrence is common in pregnancy 2, 4, 3
• Treatment failure requires culture-guided therapy with an alternative agent for 7 days 1

Acute Pyelonephritis in Pregnancy

• Pyelonephritis is the most common medical cause of hospitalization in pregnancy and carries significant maternal-fetal risk including preterm labor 2, 3
• Initial parenteral therapy is required: ceftriaxone 1-2g IV daily, cefotaxime 2g IV three times daily, or amoxicillin plus gentamicin 1, 6, 3
• Fluoroquinolones (ciprofloxacin, levofloxacin) should NOT be used in pregnant women despite being first-line for pyelonephritis in non-pregnant patients 1, 3
• Transition to oral therapy (amoxicillin, cephalosporins based on susceptibilities) after 24-48 hours afebrile, completing 7-14 days total 6, 3
• Ultrasound (not CT) is the imaging modality of choice if obstruction or complications are suspected, to avoid fetal radiation exposure 1

Common Pitfalls to Avoid

• Using trimethoprim-sulfamethoxazole without considering trimester-specific risks 1
• Prescribing nitrofurantoin without screening for G6PD deficiency 3
• Failing to obtain post-treatment urine culture to confirm eradication 2, 4
• Treating asymptomatic bacteriuria with the same casual approach as in non-pregnant women—pregnancy is one of the few conditions where ASB treatment is clearly indicated 1
• Using fluoroquinolones for pyelonephritis in pregnancy as you would in non-pregnant women 1, 3