What is the recommended screening and treatment approach for asymptomatic bacteriuria in pregnant women, particularly those with a history of urinary tract infections (UTIs) or other predisposing conditions?

Screening and Treatment of Asymptomatic Bacteriuria in Pregnancy

All pregnant women should be screened for asymptomatic bacteriuria with a urine culture at 12-16 weeks' gestation (or at the first prenatal visit if later) and treated with 4-7 days of antibiotics if positive. 1

Screening Protocol

Use urine culture as the screening test—not urinalysis or dipstick. Standard urinalysis tests (dipstick and microscopy) have poor positive and negative predictive values for detecting bacteriuria in asymptomatic persons, and no currently available screening test has sufficient sensitivity to replace urine culture in pregnancy. 1, 2

Timing and Method

• Obtain a clean-catch urine specimen for culture at 12-16 weeks' gestation or at the first prenatal visit if later. 1, 3
• A single screening culture at this initial visit is the standard approach. 1, 2
• The diagnostic threshold is ≥100,000 CFU/mL on urine culture. 2, 4

Special Considerations for High-Risk Women

While universal screening is recommended, pregnant women with prior UTI history, diabetes mellitus, urinary tract abnormalities, immunosuppression, or history of preterm birth warrant particular attention, as these risk factors increase susceptibility to complications. 5 However, this does not change the universal screening recommendation—all pregnant women should still be screened regardless of risk factors. 1

Why Screen and Treat?

The evidence supporting screening and treatment is compelling:

• Untreated asymptomatic bacteriuria leads to pyelonephritis in 20-35% of pregnant women, compared to only 1-4% when treated. 3, 4
• Treatment reduces preterm birth risk from approximately 53 per 1000 to 14 per 1000. 3
• Treatment reduces very low birth weight risk from approximately 137 per 1000 to 88 per 1000. 3
• Screening and treatment programs have demonstrated a reduction in pyelonephritis incidence from 1.8% to 0.6%. 6

The Infectious Diseases Society of America gives a strong recommendation with moderate-quality evidence for screening and treating asymptomatic bacteriuria in pregnancy, emphasizing the substantial net benefit. 1

Treatment Approach

When asymptomatic bacteriuria is detected, treat with 4-7 days of antimicrobial therapy directed at the cultured organism. 1, 3, 4

Antibiotic Selection

• Nitrofurantoin is often preferred due to its safety profile in pregnancy and effectiveness against common pathogens. 3
• Beta-lactam antibiotics (ampicillin or cephalexin) are safe alternatives. 3, 4
• Avoid single-dose regimens—they show lower bacteriuria clearance rates compared to short-course regimens. 3
• The optimal duration varies by antimicrobial agent; use the shortest effective course. 1

Follow-Up After Treatment

• Obtain a follow-up urine culture after completing antibiotics to confirm clearance. 3
• Continue periodic screening with urine cultures throughout the remainder of pregnancy after any treated episode, as recurrence is common. 3, 4
• There is insufficient evidence to recommend routine repeat screening for women with an initial negative culture who have not been treated. 1

Common Pitfalls to Avoid

• Do not rely on urinalysis alone. Pyuria screening has only ~50% sensitivity for identifying bacteriuria in pregnant women and is unreliable as a standalone test. 2 Pyuria without bacteriuria does not warrant treatment. 4
• Do not treat based on a single positive culture without confirmation unless the patient is symptomatic. The formal definition requires two consecutive voided specimens with the same organism at ≥10^5 CFU/mL. 4
• Do not skip follow-up cultures after treatment. Recurrence is common and requires re-treatment to prevent progression to pyelonephritis. 3
• Do not extrapolate pregnancy guidelines to other populations. The recommendation to screen and treat applies specifically to pregnant women—screening is not recommended for diabetic women, elderly patients, or other non-pregnant populations. 1, 7, 8

Emerging Considerations

A recent Dutch study suggested that nontreatment might be acceptable for selected low-risk women, but the IDSA committee concluded that further evaluation in other populations is necessary before changing the universal screen-and-treat recommendation. 1, 3 Until more evidence emerges, the standard of care remains universal screening and treatment for all pregnant women with asymptomatic bacteriuria. 1, 3