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

UTI in Pregnancy Treatment Algorithm

Immediate Diagnostic Steps

All pregnant women with suspected UTI must have a urine culture obtained before initiating antibiotics 1, 2. Dipstick testing alone is inadequate with only 50% sensitivity and should not replace culture 1, 2.

Screening Protocol

• Screen all pregnant women at 12-16 weeks gestation with urine culture for asymptomatic bacteriuria 1, 2
• Pregnancy is the one clinical scenario where asymptomatic bacteriuria must always be treated—untreated bacteriuria increases pyelonephritis risk 20-30 fold (from 1-4% with treatment to 20-35% without) 1, 2
• Treatment reduces preterm delivery and low birth weight 1

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First-Line Antibiotic Selection by Trimester

First Trimester (Weeks 1-13)

Nitrofurantoin is the first-line agent for uncomplicated lower UTI in the first trimester 1, 2:

• Nitrofurantoin 50-100 mg four times daily for 7 days 1, 2
• Alternative: Fosfomycin trometamol 3g single dose 1, 2
• Alternative: Cephalexin 500 mg four times daily for 7 days 1

Avoid in first trimester 1, 2:

• Trimethoprim-sulfamethoxazole (teratogenic risk including neural tube defects) 1, 3
• Fluoroquinolones (fetal cartilage toxicity) 1, 2

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Second Trimester (Weeks 14-27)

Nitrofurantoin remains first-line 1, 2:

• Nitrofurantoin 50-100 mg four times daily for 7 days 1, 2
• Fosfomycin trometamol 3g single dose 1, 2
• Cephalosporins (cephalexin, cefpodoxime, cefuroxime) for 7-14 days 1

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Third Trimester (Weeks 28-40)

Avoid nitrofurantoin near term; switch to cephalosporins 1:

• Cephalexin 500 mg four times daily for 7-14 days is first-line 1
• Alternative: Amoxicillin-clavulanate if organism susceptible 1, 4
• Alternative: Fosfomycin 3g single dose (limited data but acceptable) 1

Critical caveat: Nitrofurantoin should not be used near delivery due to risk of hemolytic anemia in the newborn 1.

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Treatment Duration

Standard duration is 7-14 days for symptomatic UTI 1, 2:

• 7-day courses are standard despite insufficient evidence for shorter regimens 1
• Single-dose or 3-day regimens have inadequate supporting data in pregnancy 1
• Asymptomatic bacteriuria: 4-7 days or single-dose fosfomycin 1, 2

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Special Clinical Scenarios

Suspected Pyelonephritis

Do not use nitrofurantoin—it does not achieve therapeutic blood concentrations 1:

• Initial parenteral cephalosporin or ampicillin-gentamicin 1
• Transition to oral cephalosporin after clinical improvement 1
• Total course: 14 days 1

Group B Streptococcus (GBS) Bacteriuria

Any concentration of GBS in urine requires treatment 1:

• Treat at time of diagnosis with appropriate antibiotic 1
• Patient also requires intrapartum GBS prophylaxis during labor 1

Penicillin Allergy

Cephalosporins are safe in most penicillin-allergic patients 1:

• Only 10% of penicillin-allergic patients react to cephalosporins 1
• Assess anaphylaxis risk; if low, cephalosporins are appropriate 1
• If high anaphylaxis risk: use nitrofurantoin (first/second trimester) or fosfomycin 1, 2

Recurrent UTI

Consider prophylactic antibiotics for remainder of pregnancy 1, 5:

• Cephalexin 250 mg post-coital or daily 1, 5
• Nitrofurantoin 50 mg post-coital (avoid near term) 5

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Post-Treatment Management

Mandatory follow-up culture 1-2 weeks after completing therapy to confirm cure 1, 2:

• This is essential in pregnancy due to high risk of treatment failure and complications 1, 2
• Do not perform repeated surveillance testing after initial cure—this fosters resistance 1

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Critical Pitfalls to Avoid

• Never delay treatment—delaying increases pyelonephritis and adverse pregnancy outcomes 1
• Never use fluoroquinolones (ciprofloxacin, levofloxacin) at any point in pregnancy 1, 2
• Never use trimethoprim-sulfamethoxazole in first trimester due to teratogenic risk 1, 3
• Never use nitrofurantoin for pyelonephritis—inadequate blood levels 1
• Never use nitrofurantoin near delivery—risk of neonatal hemolysis 1
• Never rely on dipstick alone—always obtain culture 1, 2
• Never skip post-treatment culture—treatment failure is common and dangerous 1, 2

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Antibiotic Choice Must Consider Local Resistance Patterns

While the above represents guideline-recommended first-line agents, final antibiotic selection should be guided by culture results and local resistance patterns 1, 2. However, empiric therapy should not be delayed while awaiting culture results given the serious consequences of untreated UTI in pregnancy 1.