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

Treatment of UTI in Pregnancy

For pregnant women with UTI, use nitrofurantoin (50-100 mg four times daily) or fosfomycin (3g single dose) as first-line therapy in the first and second trimesters, switching to cephalexin (500 mg four times daily) in the third trimester, with treatment duration of 7-14 days. 1, 2

First-Line Antibiotic Selection by Trimester

First and Second Trimester

• Nitrofurantoin (50-100 mg four times daily for 5-7 days) is the preferred first-line agent for uncomplicated lower UTI 1, 2
• Fosfomycin trometamol (3g single dose) is an acceptable alternative with similar efficacy 1, 2
• Cephalosporins (cephalexin, cefpodoxime, cefuroxime) are appropriate alternatives if nitrofurantoin or fosfomycin cannot be used 1, 2

Third Trimester

• Cephalexin (500 mg four times daily) becomes the preferred agent as nitrofurantoin should be avoided near term 1, 2
• Fosfomycin (3g single dose) can be considered for uncomplicated lower UTI, though data is more limited 1, 2
• Amoxicillin-clavulanate (20-40 mg/kg per day in 3 doses) is appropriate if the pathogen is susceptible 1

Critical Antibiotics to Avoid

Never use these antibiotics in pregnancy:

• Fluoroquinolones (ciprofloxacin, levofloxacin) are contraindicated throughout all trimesters due to adverse effects on fetal cartilage development 1, 2, 3
• Trimethoprim-sulfamethoxazole should be avoided in the first trimester due to teratogenic effects (anencephaly, heart defects, orofacial clefts) and is contraindicated in the third trimester 1, 2, 3

Treatment Duration and Monitoring

• Standard treatment course is 7-14 days to ensure complete eradication 1, 2
• Always obtain urine culture before initiating treatment to guide antibiotic selection 1, 2
• Perform follow-up urine culture 1-2 weeks after completing treatment to confirm cure 1, 2
• Do not perform repeated surveillance testing or treat asymptomatic bacteriuria multiple times after initial treatment, as this fosters antimicrobial resistance 1

Special Clinical Scenarios

Suspected Pyelonephritis

• Do not use nitrofurantoin if pyelonephritis is suspected as it does not achieve therapeutic blood concentrations 1, 2
• Consider hospitalization with IV ceftriaxone or cefepime for upper tract involvement (fever, flank pain, nausea/vomiting) 2
• Transition to oral cephalosporins after clinical improvement 1

Asymptomatic Bacteriuria

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

Group B Streptococcus (GBS) Bacteriuria

• GBS bacteriuria at any concentration requires treatment at diagnosis plus intrapartum prophylaxis during labor 1

Recurrent UTI

• Consider prophylactic cephalexin for the remainder of pregnancy after recurrent infections 1, 2
• Postcoital prophylaxis with cephalexin (250 mg) or nitrofurantoin (50 mg) is highly effective, reducing UTI incidence from 130 infections to a single infection during pregnancy in one study 4

Common Pitfalls to Avoid

• Do not rely on pyuria alone for diagnosis - it has only 50% sensitivity for bacteriuria 1
• Do not classify pregnant women with UTI as "complicated" unless structural/functional abnormalities or immunosuppression exist - this leads to unnecessary broad-spectrum antibiotic use 1
• Despite continued use in practice, fluoroquinolones remain contraindicated even though many providers use them when suspecting pyelonephritis 3
• Nitrofurantoin and sulfonamides carry potential risks for birth defects when used in the first trimester, though nitrofurantoin remains guideline-recommended 3