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

Treatment of UTI in Pregnancy

For pregnant women with UTI, use nitrofurantoin 100 mg four times daily for 7 days as first-line treatment in the first and second trimesters, switching to cephalexin 500 mg four times daily for 7-14 days in the third trimester or when pyelonephritis is suspected. 1, 2

First-Line Antibiotic Selection by Trimester

First and Second Trimester

• Nitrofurantoin 100 mg orally four times daily for 7 days is the preferred first-line agent 1, 2
• Fosfomycin 3g single dose is an acceptable alternative for uncomplicated lower UTI 1, 2
• Avoid trimethoprim-sulfamethoxazole in the first trimester due to neural tube defect risk 1, 2

Third Trimester

• Cephalexin 500 mg orally four times daily for 7-14 days becomes first-line because nitrofurantoin should be avoided near term due to hemolytic anemia risk in the newborn 1, 2
• Cefpodoxime or cefuroxime are alternative cephalosporin options 1
• Amoxicillin-clavulanate (20-40 mg/kg per day in 3 doses) if the pathogen is susceptible 1

Critical Diagnostic Requirements

Always obtain urine culture before initiating treatment to guide antibiotic selection and confirm diagnosis 1, 2. This is non-negotiable in pregnancy.

• Screening for pyuria alone has only 50% sensitivity and is inadequate 1
• Optimal screening timing is at 12-16 weeks gestation with a single urine culture 1, 2
• Repeat urine culture 1-2 weeks after completing treatment to confirm microbiological cure 1, 2

Treatment Duration

• 7-14 day courses are recommended despite insufficient evidence for shorter regimens 1, 2
• Minimum 4-7 days for symptomatic UTI and asymptomatic bacteriuria 2
• Single-dose fosfomycin is the exception for uncomplicated cystitis 1, 2

When to Escalate to Parenteral Therapy

Use initial parenteral therapy with cephalosporins for suspected pyelonephritis or severe infection 1, 2:

• Never use nitrofurantoin for pyelonephritis as it does not achieve therapeutic blood concentrations 1
• Hospitalization is typically necessary given maternal and fetal risks 2
• Transition to oral therapy after clinical improvement 1

Special Clinical Scenarios

Group B Streptococcus (GBS) Bacteriuria

• Any concentration of GBS bacteriuria requires immediate treatment at diagnosis plus intrapartum prophylaxis during labor 1, 2
• This differs from other organisms where colony count thresholds apply 2

Asymptomatic Bacteriuria

• Pregnancy is the one clinical scenario where asymptomatic bacteriuria must always be treated 1, 2
• Untreated bacteriuria increases pyelonephritis risk 20-30 fold (from 1-4% with treatment to 20-35% without) 1, 2
• Treatment reduces premature delivery and low birth weight 1

Recurrent UTIs During Pregnancy

• Consider prophylactic cephalexin for the remainder of pregnancy after treating acute infection 1
• Post-coital prophylaxis with cephalexin 250 mg or nitrofurantoin 50 mg single dose is highly effective 3

Antibiotics to Absolutely Avoid

• Fluoroquinolones (ciprofloxacin, etc.) throughout entire pregnancy due to fetal cartilage development concerns 1, 2, 4
• Trimethoprim-sulfamethoxazole in first trimester (neural tube defects) and last trimester (kernicterus risk) 1, 2
• Nitrofurantoin near term (hemolytic anemia in newborn) 1

Common Pitfalls to Avoid

• Failing to obtain pre-treatment urine culture leads to inappropriate empiric therapy 1, 2
• Not confirming cure with post-treatment culture misses persistent infections that dramatically increase pyelonephritis risk 1, 2
• Using nitrofurantoin for suspected pyelonephritis due to inadequate blood levels 1
• Prescribing fluoroquinolones to women of reproductive age without pregnancy testing, given that 7.2% of pregnant women develop UTI and many pregnancies are unrecognized early 4

Algorithm for Antibiotic Selection

1. Obtain urine culture immediately 1, 2
2. Assess trimester and severity:
   • First/second trimester + uncomplicated lower UTI → Nitrofurantoin 100 mg QID × 7 days 1, 2
   • Third trimester + uncomplicated lower UTI → Cephalexin 500 mg QID × 7-14 days 1, 2
   • Any trimester + suspected pyelonephritis → Parenteral cephalosporin, then oral after improvement 1, 2
3. Confirm cure with repeat culture 1-2 weeks post-treatment 1, 2
4. If recurrent infections occur, initiate prophylaxis with cephalexin for remainder of pregnancy 1, 3