Asymptomatic Bacteriuria in Pregnancy

Comments from Expert Advisory Committee

  • Asymptomatic bacteriuria is the presence of 1 or more species of bacteria growing in the urine at a quantitative count of >105 colony-forming units/mL, without signs or symptoms attributable to urinary tract infection.
  • Asymptomatic bacteriuria occurs in 2% to 7% of pregnant women.
  • Antibiotic treatment of asymptomatic bacteriuria reduces the risk of pyelonephritis, low birth weight and premature labour.
  • A urine culture is usually requested early in pregnancy (12-16 weeks).
  • The presence of asymptomatic bacteriuria should be confirmed by two consecutive urine cultures (preferably within two weeks).
  • Urine culture remains the gold standard in detection of asymptomatic bacteriuria.
  • Dipstick testing is not sufficient to screen for bacterial UTIs in pregnancy.
  • A positive urine culture for bacteriuria in the second sample of urine should be treated with an appropriate antibiotic for the bacteria isolated and the trimester of pregnancy.
  • Confirm clearance with urine culture after treatment.
  • Repeat urine cultures at subsequent antenatal visits may be required for prior recurrent UTI’s, diabetes mellitus, renal anomaly.
  • Trimethoprim should not be prescribed for pregnant women with established folate deficiency, low dietary folate intake, or women taking other folate antagonists.


Drug Dose Duration +/- Notes
1st choice options- dependent on MSU cultures and susceptibility
Nitrofurantoin 50-100mg every 6 hours 7 days Avoid after 36 weeks due to risk of neonatal haemolysis
Amoxicillin* 500mg every 8 hours 7 days *Amoxicillin resistance is common – check susceptibility from MSU sample
2nd choice option- dependent on MSU cultures & susceptibility
Cefalexin 500mg every 8 hours 7 days
If further information required on treatment options, please seek specialist/microbiologist advice.

Patient Information

Safe Prescribing (visit the safe prescribing page)

Reviewed November 2021