Asymptomatic Bacteriuria in Pregnancy

Asymptomatic bacteriuria in pregnancy is growth of 10^5 colony forming units/mL or more of a single organism in urine culture from a woman with no urinary symptoms. It affects 2 to 10 percent of pregnant women and is usually Escherichia coli. It matters because 20 to 40 percent progress to pyelonephritis and it raises the risk of preterm birth and low birth weight, so screening and treatment are routine.

• Risk factors: diabetes, sickle cell trait or disease, previous urinary infection, renal anomalies, low income, multiparity.
• Screened by culture at the booking visit.
• Treatment greatly reduces pyelonephritis.

Women have no symptoms, and examination is normal. The diagnosis is made on screening.

• No dysuria, frequency or fever.
• Normal suprapubic and loin examination.
• Differential diagnosis: contaminated sample, cystitis, vaginal discharge contamination, group B streptococcus colonisation, early pyelonephritis.
• Complications: pyelonephritis, preterm birth, low birth weight, neonatal sepsis from group B streptococcus, acute kidney injury.

The approach is midstream urine culture with confirmation of a repeat sample.

• Mid stream urine culture at booking: 10^5 colony forming units/mL or more of a single organism on 2 consecutive samples, or one catheter sample with 10^2 or more.
• Dipstick has poor sensitivity in asymptomatic women and should not replace culture.
• Culture with antibiotic sensitivity results guides treatment.
• Test of cure 1 to 2 weeks after treatment, then monthly.

The principle is a short course of an antibiotic chosen by culture, followed by a test of cure.

• Supportive: oral fluids 2 to 3 litres daily; frequent voiding; hygiene advice; clean catch technique.
• Pharmacological: cefalexin 500 mg oral 6-hourly for 7 days; or nitrofurantoin 100 mg modified release oral 12-hourly for 5 days (avoid in the first trimester when alternatives exist, at term and with glucose-6-phosphate dehydrogenase deficiency); or amoxicillin 500 mg oral 8-hourly for 7 days if sensitive; or fosfomycin 3 g oral single dose; avoid trimethoprim in the first trimester, tetracyclines and fluoroquinolones; prophylaxis for recurrence: cefalexin 250 mg oral at night until 6 weeks postpartum.
• Procedures: none.
• Special groups: group B streptococcus bacteriuria is treated and also needs benzylpenicillin 5 g IV then 2.5 g 4-hourly in labour until delivery; sickle cell disease and diabetes are screened monthly.
• Red flags: fever above 38 degrees Celsius, loin pain, rigors, vomiting, contractions.
• Follow-up: culture 1 to 2 weeks after treatment and monthly to delivery; renal ultrasound for recurrent bacteriuria; review at 6 weeks postpartum.