Asymptomatic Bacteriuria in Pregnancy

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.

Doses are oral and for adults unless otherwise stated
Dosing in children quick reference dosage/weight guide
Penicillin allergy – tips on prescribing in penicillin allergy
Renal impairment dosing table
Drug interactions table. Extensive drug interactions for clarithromycin, fluoroquinolones, azole antifungals and rifampicin. Many antibiotics increase the risk of bleeding with anticoagulants
Visit the Health Products Regulatory Authority (HPRA) website for detailed drug information (summary of product characteristics and patient information leaflets). Dosing details, contraindications and drug interactions can also be found in the Irish Medicines Formulary (IMF) or other reference sources such as British National Formulary (BNF) / BNF for children (BNFC).

Reviewed November 2021

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