Urinary tract infection
Description
- Spectrum: asymptomatic bacteriuria (ASB) -> cystitis -> pyelonephritis
- All three warrant treatment in pregnancy (unlike ASB outside pregnancy)
- Pregnancy-specific significance: untreated ASB progresses to pyelonephritis in ~20-30%
Epidemiology
- ASB ~2-10% of pregnancies
- Cystitis ~1-4%
- Pyelonephritis ~1-2% - commonest non-obstetric cause of antenatal admission
- Risk factors: prior UTI, diabetes, renal tract abnormality, sickle cell trait, multiparity
Aetiopathogenesis
- Progesterone -> ureteric/bladder smooth muscle relaxation -> dec peristalsis, urinary stasis
- Gravid uterus -> mechanical compression, right-sided ureteric dilatation more than left (dextrorotation of uterus)
- Glycosuria of pregnancy -> favours bacterial growth
- E. coli ~80-90%; also Klebsiella, Proteus, Group B Streptococcus (GBS bacteriuria at any count = treat, and flags need for intrapartum GBS prophylaxis)
Diagnosis
Screening
- MSU culture at booking, all pregnant women - screens for ASB
- ASB = >=10^5 CFU/mL single organism, no symptoms
- Repeat culture each trimester if history of recurrent UTI or risk factors
Cystitis
- Dysuria, frequency, urgency, suprapubic discomfort, no systemic upset
- Urine MCS before treating
Pyelonephritis
- Fever, rigors, loin pain, nausea/vomiting, +/- cystitis symptoms
- Bloods: FBE, UEC, CRP, blood cultures if unwell, urine MCS
- Consider preterm labour, chorioamnionitis, appendicitis, placental abruption as differentials for fever + abdominal pain
Management
ASB and cystitis - empirical, then tailor to culture
- Nitrofurantoin - first-line (avoid near term - theoretical neonatal haemolysis risk with G6PD deficiency)
- Cephalexin or amoxicillin-clavulanate - alternatives
- Avoid trimethoprim in 1st trimester (folate antagonist - neural tube defect risk); avoid sulphonamides near term (kernicterus risk)
- Avoid quinolones and tetracyclines throughout pregnancy
- Course 5-7 days; test-of-cure culture 1 week after completion
Pyelonephritis
- Admit - IV antibiotics initially (e.g. IV ceftriaxone or gentamicin + amoxicillin, per local guideline)
- IV fluids, antiemetics, analgesia
- Fetal monitoring if >=24 weeks (sepsis can precipitate preterm labour)
- Step down to oral once afebrile 24-48h; total course ~10-14 days
- Recurrent pyelonephritis -> renal tract imaging (ultrasound), consider prophylactic antibiotics for remainder of pregnancy
GBS bacteriuria
- Treat the episode -> document as an indication for intrapartum IV penicillin prophylaxis, regardless of later antenatal swab results
Associations
- Preterm labour and birth
- Low birth weight
- Pyelonephritis -> sepsis, ARDS, acute kidney injury (rare but described)
- Recurrent UTI in pregnancy - consider underlying renal tract anomaly
Natural history & complications
- Treated ASB/cystitis - excellent prognosis, prevents progression to pyelonephritis
- Untreated ASB - ~20-30% progress to pyelonephritis
- Postpartum - persistent bacteriuria warrants renal tract review outside pregnancy
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