Do I treat asymptomatic bacteriuria (presence of bacteria in urine) in a pregnant patient at 36 weeks of gestation with no symptoms?

Treatment of Asymptomatic Bacteriuria in Pregnancy at 36 Weeks

Yes, you should treat asymptomatic bacteriuria in a pregnant patient at 36 weeks gestation, even with only a few bacteria on urinalysis and no symptoms, to reduce the risk of maternal and fetal complications. 1

Rationale for Treatment

Asymptomatic bacteriuria in pregnancy requires treatment regardless of gestational age due to:

• Untreated asymptomatic bacteriuria carries a 20-35% risk of developing pyelonephritis, which treatment reduces to 1-4% 1
• Treatment decreases the risk of preterm birth (from ~53 per 1000 to 14 per 1000) and very low birth weight (from ~137 per 1000 to 88 per 1000) 1
• Even at 36 weeks, pyelonephritis poses significant risks to both mother and fetus

Diagnostic Considerations

Before initiating treatment:

• Confirm the diagnosis with a urine culture, as this is the gold standard 1
• Bacteriuria is defined as:
  • 2 consecutive voided specimens with ≥10^5 CFU/mL of the same bacterial strain, OR
  • A single catheterized specimen with ≥10^2 CFU/mL of one bacterial species 1
• Note that dipstick testing alone has low sensitivity (~50%) and is not reliable for treatment decisions 1

Treatment Recommendations

For confirmed asymptomatic bacteriuria at 36 weeks:

1. First-line antibiotic options (3-7 day course based on culture and sensitivity):

   • Nitrofurantoin 100mg BID
   • Cephalexin 500mg QID
   • Ampicillin 500mg QID (if susceptible) 1

2. Antibiotics to avoid during pregnancy:

   • Fluoroquinolones
   • Tetracyclines
   • Trimethoprim-sulfamethoxazole (especially in third trimester) 1

Follow-up Protocol

After initiating treatment:

• Obtain a follow-up urine culture 1-2 weeks after completing therapy to ensure clearance 1
• If bacteriuria persists, retreat with a different antibiotic based on susceptibility testing 1
• Continue monitoring through delivery due to risk of recurrence

Common Pitfalls to Avoid

• Ignoring few bacteria: Even small amounts of bacteria in a pregnant patient warrant attention and proper culture confirmation 1
• Inadequate treatment duration: Single-dose therapy is less effective than 4-7 day regimens 1
• Inappropriate antibiotic selection: Using antibiotics with potential fetal harm or high resistance patterns 1, 2
• Failure to follow up: Not confirming clearance of bacteriuria after treatment 1

Special Considerations at 36 Weeks

While the patient is near term, treatment remains important because:

• Pyelonephritis can develop rapidly and cause serious maternal morbidity
• Even late preterm birth (before 37 weeks) carries increased risks for the newborn
• The short remaining duration of pregnancy doesn't outweigh the potential risks of untreated bacteriuria

The evidence consistently supports treating asymptomatic bacteriuria at any stage of pregnancy, including at 36 weeks, to prevent serious complications for both mother and baby.