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

Treatment of UTI During Pregnancy

Treat pregnant women with UTIs using nitrofurantoin 100 mg twice daily for 5-7 days as first-line therapy in the first and second trimesters, or cephalexin 500 mg four times daily for 7-14 days as first-line in the third trimester or when pyelonephritis is suspected. 1, 2

First-Line Antibiotic Selection by Trimester

First and Second Trimester

• Nitrofurantoin 100 mg twice daily for 5-7 days is the preferred first-line agent, with extremely low rates of serious adverse events (pulmonary toxicity 0.001%, hepatic toxicity 0.0003%) 1, 2
• Fosfomycin 3g single dose is an acceptable alternative for uncomplicated lower UTIs, though clinical data is more limited 1, 2
• Cephalosporins (cephalexin, cefpodoxime, cefuroxime) are appropriate alternatives with excellent safety profiles and adequate blood/urinary concentrations 1

Third Trimester

• Cephalexin 500 mg four times daily for 7-14 days becomes first-line, as nitrofurantoin should be avoided near term due to theoretical risk of neonatal hemolysis 1
• Fosfomycin 3g single dose can be considered for uncomplicated lower UTIs, though data is more limited than for cephalosporins 1
• Amoxicillin-clavulanate (20-40 mg/kg per day in 3 doses) is appropriate if the pathogen is susceptible 1

Critical Antibiotics to Avoid

• Avoid trimethoprim-sulfamethoxazole in the first trimester due to potential interference with folic acid metabolism and theoretical neural tube defect risk 1, 2
• Avoid trimethoprim-sulfamethoxazole in the third trimester due to risk of neonatal hyperbilirubinemia and kernicterus 2
• Avoid fluoroquinolones (ciprofloxacin) throughout all trimesters due to potential adverse effects on fetal cartilage development and arthropathy in juvenile animals 1

Treatment Duration and Monitoring

• Standard treatment course is 7-14 days for symptomatic UTI, though 4-7 days may be acceptable depending on the antimicrobial chosen 1, 2
• Single-dose therapy shows higher failure rates compared to multi-day courses and should be avoided for symptomatic infections 2
• Obtain urine culture before initiating treatment to guide antibiotic selection, as pyuria screening alone has only 50% sensitivity for identifying bacteriuria 1, 2
• Perform follow-up urine culture 1-2 weeks after completing treatment to confirm cure 1

Special Considerations for Pyelonephritis

• Do not use nitrofurantoin for suspected pyelonephritis, as it does not achieve therapeutic concentrations in the bloodstream 1
• Initial parenteral therapy may be required for severe infections or pyelonephritis, with transition to oral therapy after clinical improvement 1
• Preferred agents include amoxicillin combined with an aminoglycoside, third-generation cephalosporins, or carbapenems 3

Asymptomatic Bacteriuria Management

• All pregnant women should be screened with urine culture at 12-16 weeks gestation, as untreated bacteriuria increases pyelonephritis risk 20-30 fold (from 1-4% with treatment to 20-35% without) 1, 2
• Treat asymptomatic bacteriuria with the same antibiotic regimens as symptomatic UTI, as pregnancy is the one clinical scenario where asymptomatic bacteriuria must always be treated 1, 2
• Treatment reduces pyelonephritis risk from 20-37% to 1-6% and decreases premature delivery and low birth weight 1, 2
• Do not perform surveillance urine testing or treat asymptomatic bacteriuria repeatedly after the initial screen-and-treat approach, as this fosters antimicrobial resistance 1

Group B Streptococcus (GBS) Considerations

• GBS bacteriuria in any concentration during pregnancy requires treatment at diagnosis plus intrapartum GBS prophylaxis during labor, as it is a marker for heavy genital tract colonization 1

Recurrent UTI Prophylaxis

• For recurrent UTIs, consider prophylactic cephalexin for the remainder of pregnancy 1

Common Pitfalls to Avoid

• Do not classify pregnant women with UTIs as "complicated" unless they have structural/functional urinary tract abnormalities or immunosuppression, as this leads to unnecessary broad-spectrum antibiotic use 1
• Do not delay treatment in pregnant women with symptomatic UTI, as this increases the risk of pyelonephritis and adverse pregnancy outcomes 1
• Antibiotic choice must consider local resistance patterns and patient-specific factors such as allergies 1
• For penicillin-allergic patients, assess anaphylaxis risk—only 10% of penicillin-allergic patients have reactions to cephalosporins, making them safe if not high-risk 1