What is the appropriate treatment for a urinary tract infection in a pregnant woman?

Treatment of Urinary Tract Infections in Pregnancy

Nitrofurantoin (50-100 mg four times daily for 7 days) or fosfomycin (3g single dose) are the first-line antibiotics for treating UTIs in pregnant women, with cephalosporins (such as cephalexin 500 mg four times daily for 7-14 days) as appropriate alternatives. 1

Critical Context: Why Treatment Cannot Be Delayed

• Untreated bacteriuria increases pyelonephritis risk 20-30 fold, escalating from 1-4% with treatment to 20-35% without treatment 2, 1
• Treatment reduces premature delivery and low birth weight infants 2, 1
• Pregnancy is the one clinical scenario where even asymptomatic bacteriuria must always be treated due to significant risk for progression to pyelonephritis and adverse pregnancy outcomes 2, 1
• Implementation of screening programs decreased pyelonephritis rates from 1.8-2.1% to 0.5-0.6% 2

First-Line Antibiotic Selection by Trimester

First Trimester

• Nitrofurantoin is the preferred first-line agent (50-100 mg four times daily for 7 days) 1
• Fosfomycin trometamol (3g single dose) is an acceptable alternative 1
• Cephalosporins (cephalexin, cefpodoxime, or cefuroxime) are safe and effective alternatives 1
• Avoid trimethoprim-sulfamethoxazole in the first trimester due to potential teratogenic effects (risk of anencephaly, heart defects, and orofacial clefts) 1
• Avoid fluoroquinolones throughout pregnancy due to potential adverse effects on fetal cartilage development 1

Second Trimester

• Same antibiotic options as first trimester 1
• Nitrofurantoin, fosfomycin, or cephalosporins remain first-line 1

Third Trimester

• Cephalexin 500 mg four times daily for 7-14 days is the preferred first-line alternative 1
• Avoid nitrofurantoin near term (after 36 weeks) due to theoretical risk of hemolytic anemia in the newborn 1
• Fosfomycin (3g single dose) can be considered for uncomplicated lower UTIs, though clinical data is more limited 1
• Amoxicillin-clavulanate (20-40 mg/kg per day in 3 doses) is appropriate if the pathogen is susceptible 1

Treatment Duration

• 7-14 days for symptomatic UTI or cystitis 1
• 4-7 days for asymptomatic bacteriuria, with the shortest effective course preferred 1
• Historical data consistently demonstrates efficacy with these durations, reducing pyelonephritis risk from 20-35% to 1-4% 2, 1

Diagnostic Approach: What You Must Do Before Treating

• Obtain urine culture before initiating treatment to guide antibiotic selection and confirm diagnosis 1
• Optimal screening timing is at 12-16 weeks gestation with a single urine culture 1
• Do not rely on dipstick testing alone—it has only 50% sensitivity for detecting bacteriuria in pregnant women 1
• Screening for pyuria alone is inadequate and unreliable in pregnancy 1
• For symptomatic UTI, initiate empiric treatment immediately without waiting for culture results, but the culture must still be obtained 1

Treatment of Pyelonephritis in Pregnancy

• Initial parenteral therapy with ceftriaxone (1-2g daily) or cefepime (1-2g twice daily) for hospitalized pregnant women 1
• Transition to oral cephalosporin therapy after clinical improvement 1
• Complete a total course of 7-14 days 1
• Do not use nitrofurantoin for pyelonephritis—it does not achieve therapeutic concentrations in the bloodstream 1

Follow-Up and Monitoring

• Obtain follow-up urine culture 1-2 weeks after completing treatment to confirm cure 1
• If symptoms persist or recur within 2 weeks, obtain repeat culture with antimicrobial susceptibility testing and retreat with a 7-day course of an alternative antibiotic 1
• Do not perform surveillance urine testing or treat asymptomatic bacteriuria repeatedly after the initial screen-and-treat approach, as this fosters antimicrobial resistance 1

Special Consideration: Group B Streptococcus (GBS)

• GBS bacteriuria in any concentration during pregnancy is a marker for heavy genital tract colonization and requires treatment 1
• Women with GBS bacteriuria during pregnancy should receive appropriate treatment at the time of diagnosis 1
• These women automatically qualify for intrapartum GBS prophylaxis during labor—they do not need vaginal-rectal screening at 35-37 weeks 1

Recurrent UTIs in Pregnancy

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

Common Pitfalls to Avoid

• Do not delay treatment waiting for culture results in symptomatic patients—initiate empiric therapy immediately while awaiting culture 1
• Do not use fluoroquinolones (ciprofloxacin, levofloxacin) at any point during pregnancy despite their effectiveness in non-pregnant patients 1
• Do not use trimethoprim-sulfamethoxazole in the first trimester and it is contraindicated in the last trimester 1
• Do not treat asymptomatic bacteriuria with nitrofurantoin if pyelonephritis is suspected—use cephalosporins or parenteral therapy instead 1
• 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