What is the recommended treatment for a urinary tract infection (UTI) in a pregnant woman?

Treatment of Urinary Tract Infections in Pregnancy

For symptomatic UTIs in pregnant women, treat with cephalexin 500 mg four times daily for 7-14 days as first-line therapy, or nitrofurantoin for uncomplicated lower tract infections in the first and second trimesters, always obtaining a urine culture before initiating treatment. 1, 2

Diagnostic Approach

Always obtain a urine culture before starting antibiotics to guide therapy and allow adjustment if the organism proves resistant to empiric treatment. 1, 2 This is critical in pregnancy because:

• Untreated bacteriuria increases pyelonephritis risk 20-30 fold (from 20-35% to 1-4% with treatment). 1
• Treatment reduces premature delivery and low birth weight. 1
• Pregnant women require urine culture even with typical symptoms, unlike non-pregnant women where empiric treatment is acceptable. 3

First-Line Antibiotic Selection by Trimester

First Trimester

• Nitrofurantoin (50-100 mg four times daily for 5 days) is the preferred first-line agent. 1
• Fosfomycin trometamol (single 3g dose) is an acceptable alternative. 3, 1
• Avoid trimethoprim and trimethoprim-sulfamethoxazole due to teratogenic effects in the first trimester. 1, 2

Second and Third Trimesters

• Cephalexin 500 mg four times daily for 7-14 days is the preferred first-line therapy. 1, 2
• Alternative cephalosporins include cefpodoxime or cefuroxime. 1, 2
• Avoid nitrofurantoin in the third trimester (particularly near term) due to risk of hemolytic anemia in the newborn. 1
• Fosfomycin (single 3g dose) can be considered for uncomplicated lower UTIs, though data is more limited than for cephalosporins. 1, 2

Throughout Pregnancy

• Avoid fluoroquinolones (ciprofloxacin, levofloxacin) due to adverse effects on fetal cartilage development. 1, 2

Treatment Duration and Follow-Up

• Standard treatment duration is 7-14 days to ensure complete eradication, longer than in non-pregnant women. 1, 2
• Repeat urine culture 1-2 weeks after completing treatment to confirm cure, as incompletely treated UTI can progress to pyelonephritis. 1, 2
• For asymptomatic bacteriuria, screen and treat with standard short-course treatment or single-dose fosfomycin. 3

Special Considerations

Suspected Pyelonephritis (Upper Tract Involvement)

• Look for fever, flank pain, nausea/vomiting, or costovertebral angle tenderness. 2
• Do not use nitrofurantoin as it does not achieve therapeutic blood concentrations. 1
• Hospitalize and initiate IV therapy with ceftriaxone or cefepime. 2
• Transition to oral cephalosporins after clinical improvement. 1

Penicillin Allergy

• Only 10% of penicillin-allergic patients have cross-reactivity to cephalosporins. 1
• Assess for high-risk anaphylaxis history; if low risk, cephalosporins remain safe. 1
• If true severe allergy, use fosfomycin or nitrofurantoin (trimester-appropriate). 1

Group B Streptococcus (GBS) Bacteriuria

• GBS bacteriuria at any concentration indicates heavy genital colonization. 1
• Treat at diagnosis AND provide intrapartum GBS prophylaxis during labor. 1

Recurrent UTIs in Pregnancy

• Consider prophylactic cephalexin for the remainder of pregnancy after treating acute infection. 1, 2

Common Pitfalls to Avoid

• Do not treat asymptomatic bacteriuria without a positive culture, as this fosters antimicrobial resistance. 3
• Do not classify pregnancy UTIs as "complicated" simply because the patient is pregnant—this leads to unnecessary broad-spectrum antibiotics. Reserve "complicated" for structural abnormalities, immunosuppression, or nephrolithiasis. 3
• Do not use short 3-day courses commonly used in non-pregnant women; pregnancy requires 7-14 days. 1, 2
• Do not skip the follow-up culture—failure to confirm eradication risks progression to pyelonephritis with serious maternal and fetal consequences. 1, 2