What is the recommended treatment for a 35-week pregnant woman with a urinary tract infection (UTI)?

Treatment of Bladder Infection at 35 Weeks Pregnancy

For a pregnant woman at 35 weeks with a bladder infection, initiate oral cephalexin 500 mg four times daily for 7-14 days immediately after obtaining a urine culture, and ensure she receives intravenous penicillin G or ampicillin prophylaxis during labor if Group B Streptococcus is identified. 1

Immediate Management Steps

Obtain Urine Culture Before Treatment

• A urine culture must be obtained before initiating empirical antibiotic therapy to guide subsequent treatment decisions and identify any Group B Streptococcus colonization 1
• Urine dipstick testing is unreliable in pregnancy, with only 50% sensitivity for detecting bacteriuria, so culture is mandatory regardless of dipstick results 1

First-Line Antibiotic Options

Cephalosporins (Preferred):

• Cephalexin 500 mg orally four times daily for 7-14 days is the recommended first-line treatment 1
• Cephalosporins achieve adequate blood and urinary concentrations with excellent safety profiles in pregnancy 1
• Alternative cephalosporins include cefpodoxime or cefuroxime if cephalexin is unavailable 1

Alternative Options:

• Nitrofurantoin 50-100 mg four times daily for 7 days is acceptable for uncomplicated lower UTI, though it should be avoided near term (after 36 weeks) due to theoretical risk of neonatal hemolysis 1, 2
• Fosfomycin 3g single oral dose can be considered, though clinical data for third trimester use is more limited than for cephalosporins 1
• Amoxicillin-clavulanate 20-40 mg/kg per day in 3 divided doses if the pathogen is susceptible 1

Critical Special Consideration: Group B Streptococcus

If GBS is Identified in Urine Culture

• Any concentration of GBS in urine during pregnancy requires both immediate treatment AND mandatory intravenous antibiotic prophylaxis during labor, regardless of whether the UTI was treated earlier 3
• GBS bacteriuria at any concentration indicates heavy genital tract colonization and significantly increases the risk of early-onset neonatal GBS disease 3
• Women with GBS bacteriuria do not need vaginal-rectal screening at 35-37 weeks—they automatically qualify for intrapartum prophylaxis 4, 3

Intrapartum Prophylaxis Regimen for GBS

• Penicillin G 5 million units IV initially, then 2.5 million units IV every 4 hours until delivery (preferred) 3
• Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery (acceptable alternative) 3
• For penicillin allergy without high anaphylaxis risk: Cefazolin 2 g IV initially, then 1 g IV every 8 hours 3
• For high anaphylaxis risk: Clindamycin 900 mg IV every 8 hours (if susceptible) or vancomycin 1 g IV every 12 hours 3
• Prophylaxis must be administered at least 4 hours before delivery for maximum effectiveness (78% reduction in neonatal GBS disease) 3

Antibiotics to Avoid in Third Trimester

• Trimethoprim-sulfamethoxazole is contraindicated in the third trimester due to risk of neonatal hyperbilirubinemia and kernicterus 1, 5
• Fluoroquinolones (ciprofloxacin, levofloxacin) must be avoided throughout pregnancy due to potential adverse effects on fetal cartilage development 1, 2
• Nitrofurantoin should be avoided after 36 weeks gestation due to theoretical risk of neonatal hemolytic anemia 1

Treatment Duration and Follow-Up

• The recommended treatment course is 7-14 days to ensure complete eradication of infection 1
• A follow-up urine culture 1-2 weeks after completing treatment is recommended to confirm cure 1
• For recurrent UTIs, consider prophylactic cephalexin for the remainder of pregnancy 1

Clinical Context: Why Treatment is Urgent

• Untreated bacteriuria increases pyelonephritis risk 20-30 fold (from 1-4% with treatment to 20-35% without treatment) 1
• Treatment reduces premature delivery and low birth weight infants 1
• Even asymptomatic bacteriuria must be treated during pregnancy due to significant risk of progression to pyelonephritis and adverse pregnancy outcomes 1

Common Pitfalls to Avoid

• Do not assume treating the UTI eliminates the need for intrapartum GBS prophylaxis—treating the UTI does not eliminate GBS colonization from the genitourinary tract, and recolonization after oral antibiotics is typical 3
• Do not rely on negative dipstick to rule out UTI—the presence of symptoms warrants culture and empirical treatment regardless of dipstick results 1
• Do not use agents that don't achieve therapeutic blood concentrations (like nitrofurantoin) if pyelonephritis is suspected—these patients require cephalosporins or initial parenteral therapy 1
• Ensure the anticipated site of delivery is notified if GBS is identified, as this information is critical for intrapartum management 3