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T3.2 Urinary Tract Infection Management in Pregnancy – Comprehensive Study Notes

Scope & Learning Objectives

  • Distinguish between:
    • Asymptomatic bacteriuria (ASB) – positive culture, no clinical signs
    • Symptomatic UTI (cystitis) – positive culture plus clinical manifestations; risk of rapid progression to pyelonephritis
  • Understand pregnancy-specific anatomy/physiology that increases UTI risk
  • Master history-taking, screening, sample collection, result interpretation, antibiotic selection, follow-up and referral pathways
  • Emphasise culturally safe, informed-choice, whanau-centred care at every step

Normal & Pregnancy-Altered Urinary Physiology

  • Hormones
    • Progesterone → smooth-muscle relaxation → ureteric & renal-pelvis dilatation
    • Oestrogen contributes but progesterone predominates
  • Mechanical & functional sequelae
    • Bladder tone ↓ → ↑ residual volume
    • Vesico-ureteric reflux ↑
    • Urinary flow rate ↓ → stasis → bacterial proliferation
  • Renal haemodynamics
    • Renal plasma flow ↑ by 60!–!80\% (2nd trimester)
    • Glomerular filtration rate ↑ by 40\% → ↑ urine output & nocturia
  • Immunology
    • Physiological immunosuppression in pregnancy → susceptibility to infection

Comprehensive History-Taking

  • Obtain/refresh history at booking & each contact
    • Previous UTIs: onset age, recurrence pattern, management strategies
    • Known risk factors: diabetes, renal anomalies, incontinence, sexual practices, hygiene
    • Medication allergies / hypersensitivities (esp. penicillins, sulpha, nitrofurantoin)
    • Obstetric history: pre-term labour, pyelonephritis, GBS colonisation
  • Educate on hygiene (front-to-back wiping), fluid intake, voiding frequency

Screening & Investigation Schedule

  • Offer mid-stream urine (MSU) culture to all pregnant people at booking (ideally 12!–!16 w, can be earlier)
  • Additional MSU if:
    • New urinary symptoms
    • Previous positive culture (test-of-cure \approx 7 d post-treatment)
    • Recurrent UTIs → consider monthly cultures
  • Turn-around times
    • Microscopy (cells) < 24 h
    • Culture & sensitivities 24!–!48 h

Sample Collection – Key Teaching Points

  • Purpose: avoid skin/epithelial contamination → single-organism, significant-count result
  • Instructions
    • External genital cleansing (water or provided wipe)
    • Part fore-stream into toilet, collect mid-stream
    • Keep lab transit < 2 h (or refrigerate 4 °!C up to 24 h)
  • Contamination indicators: mixed growth, >10 epithelial cells/HPF → repeat

Asymptomatic Bacteriuria (ASB)

  • Definition: \ge 10^{5} CFU/ml of a single organism on culture without symptoms
  • Prevalence: 5!–!10\% of pregnancies; \tfrac{1}{3} will develop symptomatic infection/pyelonephritis if untreated
  • Maternal–fetal risks if untreated
    • Symptomatic UTI → pyelonephritis
    • Pre-term labour, low birth-weight
  • Diagnostic clues
    • Dipstick often negative for leukocytes/nitrites
    • MSU culture is essential (screening only way to detect)
  • Management
    • Wait for culture & sensitivity (C&S) before prescribing (no symptoms → can safely delay 48 h)
    • Choose narrowest-spectrum antibiotic effective and pregnancy-safe
    • 1st line (if S on C&S & no penicillin allergy): Amoxicillin 500 mg 8-hourly \times 5 d
    • Alternatives (trimester-specific):
      • Nitrofurantoin 50 mg QID 5 d (avoid >38 w due to neonatal haemolysis)
      • Trimethoprim 300 mg nocte 3 d (contra-indicated < 14 w due to folate antagonism)
    • Test-of-cure MSU 7 d post-course

Symptomatic UTI (Cystitis)

  • Clinical features
    • Dysuria, frequency, urgency, suprapubic pain, cloudy/foul urine
    • May overlap with normal pregnancy frequency → maintain high suspicion
  • Assessment (must be face-to-face)
    • Full vitals: T, P, R, BP
    • Abdominal palpation: uterine tenderness, contractions
    • Dipstick: leukocytes (L), nitrites (N) (note: gram-positive UTIs may give L++ but N-)
    • Collect urgent MSU before first dose if possible, but do not delay treatment
  • Empirical treatment principles
    • Use broad-spectrum agent covering E.coli (~80\% of cases)
    • Amoxicillin not 1st-line (≈48.8\% resistance)
  • Empirical options (uncomplicated cystitis)
    • Nitrofurantoin 50 mg QID \times 5 d (avoid >38 w)
    • Trimethoprim 300 mg nocte \times 3 d (not < 14 w)
    • Amoxicillin+Clavulanate (Augmentin) 625 mg TID \times 5 d (avoid threatened pre-term labour; NEC risk)
    • Cefaclor 500 mg TID \times 5 d (reserve; discuss with team)
  • Counsel woman that antibiotic may change once C&S returns; shared decision-making
  • Follow-up
    • Review C&S at 48 h → adjust if resistant
    • Repeat MSU 7 d after course end
    • Recurrence ⇒ monthly screening / specialist consult

Pyelonephritis – Red Flags & Emergency Pathway

  • Incidence \approx 2\% pregnancies; can evolve from untreated cystitis or present de novo
  • Symptoms/signs
    • Fever/rigors, flank (costovertebral) pain, nausea/vomiting, tachycardia, uterine irritability
  • Immediate actions
    • Urgent face-to-face assessment; basic obs as above
    • Take MSU ± blood cultures, FBC, UE
    • Hospital referral/transfer of care – IV broad-spectrum antibiotics; fluid resuscitation; fetal monitoring
  • Complications
    • Septicaemia, ARDS, pre-term labour, IUGR, perinatal death, maternal cerebral palsy risk for infant (secondary to sepsis-related hypoxia)

Common Uropathogens & Frequency

  • E.\ coli \approx 70!–!90\%
  • Proteus\ mirabilis
  • Klebsiella\ spp.
  • Enterococcus\ spp.
  • Group B Streptococcus (GBS) – low but significant
  • Candida – rare; consider immunosuppression/prolonged hospitalisation

Group B Streptococcus in Urine

  • Any quantity in MSU deemed clinically significant in pregnancy
  • Management
    • Treat as UTI (regimen per sensitivity)
    • Automatic candidate for intrapartum IV prophylaxis (no need for 35!–!37 w vaginal–rectal swab)

Sterile Pyuria (Leukocyturia with Negative Culture)

  • High leukocytes (>100/HPF) + no growth → consider Chlamydia trachomatis
  • Lab will query clinician for CT-NAAT if not pre-authorised
  • Essential to have prospective informed consent at booking (possibility of STI detection)
  • Management: discuss results; partner notification & treatment; antibiotics per guidelines (e.g. azithromycin)

Antibiotic Selection Matrix (Gestation vs Safety)

  • 1st Trimester (≤13 w):
    • Avoid trimethoprim (folate antagonism)
    • Nitrofurantoin acceptable (but monitor G6PD if relevant)
  • 2nd Trimester: most agents acceptable
  • 3rd Trimester (>38 w):
    • Avoid nitrofurantoin (neonatal haemolysis)
    • Avoid sulphonamides (kernicterus risk)

Follow-Up & Recurrence Algorithm

  • Single treated episode, negative test-of-cure → routine care
  • Recurrent UTI (≥2 cultured episodes):
    • Monthly MSU
    • Consider low-dose nightly antibiotic prophylaxis (specialist)
    • Evaluate for structural anomalies, diabetes, hygiene issues

Communication, Consent & Cultural Safety

  • Provide full information at initial MSU offer: purpose, possible findings (incl. STIs), treatment pathways, right to decline
  • Re-visit discussions when new results arise; seek renewed consent for additional tests (e.g. CT-NAAT)
  • Employ face-to-face assessments for symptomatic cases; allow whanau support; respect cultural sensitivities around urine collection
  • Document all discussions, decisions, allergies, treatment plans

Referral & Escalation Summary

  • Consult / Discuss (Obstetric / GP / ID):
    • Allergy limiting antibiotic options
    • Recurrent UTIs despite guideline therapy
    • ASB unresponsive after 2 courses
  • Transfer of Care (Urgent):
    • Pyelonephritis / sepsis suspicion
    • UTI with pre-term contractions or haemodynamic instability

Quick Reference Cheat-Sheet

  • Booking MSU for every pregnant woman (cost-effective vs pre-term NICU stay)
  • ASB → wait C&S, narrow-spectrum, 5 d, repeat MSU in 7 d
  • Symptomatic → empirical broad-spectrum immediately, adjust at 48 h, treat 3!–!5 d
  • Avoid trimethoprim < 14 w & nitrofurantoin >38 w
  • Pyelonephritis = hospital + IV
  • GBS in urine = treat now and intrapartum IV prophylaxis
  • Sterile pyuria = think chlamydia

Ethical & Practical Implications

  • Antimicrobial stewardship: shortest effective course (typically 3–5 d) to curb resistance
  • Balance teratogenic risk vs infection morbidity; engage woman in shared decision-making
  • Cost–benefit: screening cheaper than managing pyelonephritis/perinatal sequelae

Reference Pointers (full list in course pack)

  • Cochrane Review on ASB treatment duration (2010)
  • Systematic Review of antibiotic class efficacy (2011)
  • NZ/Aus antimicrobial pregnancy categorisations
  • ORACLE trial – augmentin & pre-term labour NEC association
  • Local referral guidelines & NZCOM consensus statements