Fetal diagnostic scans are undertaken at 18–20 weeks and may be repeated at 32–34 weeks

18–20 week scan

Possible urinary tract abnormalities include:

Kidneys

• Renal agenesis +/- oligohydramnios – Potter sequence
• Multi-cystic dysplastic kidney (MCDK), check other kidney for normal appearance
• Solitary kidney
• Abnormal position (e.g. pelvic) or shape (e.g. horseshoe) 
• Kidneys with echo-bright parenchyma (suspect cystic diseases)

Collecting system/tubes

• Unilateral or bilateral renal pelvic dilatation (RPD)/pelviectasis
• Measured in antero-posterior diameter (APD)
  
  • mild: RPD 5–9 mm 
  • moderate: RPD 10–14 mm 
  • severe: RPD ≥15 mm 
• Unilateral or bilateral dilated calyces or ureter 

Bladder (dialated or thick walled; ureterocoele in bladder) 32–34 week scan

• To clarify urinary tract abnormalities found in early fetal scans
• Assess severity of RPD/pelviectasis:
  
  • normal: RPD <7 mm
  • mild: RPD 7–9 mm
  • moderate: RPD 10–14 mm. If bilateral, suspect critical obstruction
  • severe: RPD ≥15 mm. Suspect critical obstruction 
  • calyceal dilatation: often indicates severity; may suggest obstruction
• Unilateral/bilateral dilated ureter(s) - suspect obstruction or vesico-ureteric reflux (VUR) 
• Thick-walled bladder, suspect outlet obstruction
• Dilated bladder, suspect poor emptying
• Ureterocoele, suspect duplex system on that side

Comunication

• Provide mother with an information leaflet, if available in your hospital, about this antenatal anomaly and proposed plan of management after birth 

Undications for intervention

Urgent

• Bilateral RPD ≥10 mm +/- thick-walled bladder: suspect posterior urethral valve (boys)
• Unilateral RPD ≥15 mm, suspect pelvi-ureteric junction (PUJ) obstruction
• Significant abnormalities of kidney(s)/urinary tract – if risk of renal insufficiency
  
  • check serum potassium, blood gas for metabolic acidosis and serum creatinine

Non-urgent

• All other abnormalities of urinary tract in the antenatal scan

For urgent indications

• If posterior urethral valve (PUV)/PUJ obstruction suspected, check urine output/stream and monitor weight trend
• Arrange urgent KUB ultrasound scan within 24–48 hr (minimal milk intake may underestimate the size of renal pelvis, but
  • do not delay if there is gross dilatation)
  • If postnatal scan raises suspicion of posterior urethral valve (dilated ureters + thick walled bladder)
    check serum creatinine 
  • arrange urgent micturating cysto-urethrogram (MCUG) 
  • after confirmation by MCUG, refer baby urgently to paediatric urologist 

•  
• If unilateral RPD ≥20 mm (suggestive of PUJ obstruction) discuss with urologist and arrange MAG3 renogram as soon as
  • possible/as advised by urologist 
• Significant abnormalities of kidney(s)/urinary tract – if risk of renal insufficiency:
  
  • check serum potassium, blood gas for metabolic acidosis and serum creatinine
  • start trimethoprim 2 mg/kg as single night-time dose
• Discuss with consultant before discharge

For non-urgent indications

• Renal ultrasound scan at aged 2–6 weeks 
• Consultant review with results 

Antibiotic prophylaxis

• For RPD ≥10 mm, give trimethoprim 2 mg/kg as single night-time dose until criteria for stopping are met (see below)

• Subsequent management depends on findings of ultrasound scan at 2–6 weeks 

Severe pelvectasis (RPD ≥15 mm)

• Arrange MAG3 scan – timing depends on severity of obstruction – as soon as possible if RPD ≥20 mm 

  • if MAG3 scan shows obstructed pattern, discuss with paediatric urologist

• Repeat ultrasound scan at aged 3–6 months (depending on cause of dilatation, a complete obstruction requires closer monitoring)

• Continue antibiotic prophylaxis until advised otherwise by urologist 

Moderate unilateral pelviectasis (RPD 10–14 mm) and/or ureteric dilatation

• Presumed mild obstruction or VUR

• If RPD increases beyond 15 mm, arrange MAG3 scan 

• Continue prophylaxis for VUR ≥grade 4 (marked dilatation of ureter and calyces) until child is continent (out of nappies)

• Repeat scan every 6 months until RPD <10 mm, then follow advice below 

Normal or mild isolated pelviectasis (RPD <10 mm)

• Stop antibiotic prophylaxis 
• Repeat scan after 6 months
  
  • if 6 month scan normal or shows no change and there have been no urinary tract infections (UTIs), discharge
  • If unwell, especially pyrexial without obvious cause, advise urine MC&S 

MCDK

• DMSA to clarify nil function of MCDK and normal uptake pattern of other kidney
• Repeat ultrasound scan 6–12 monthly to observe involution of kidney (may take several years)
• Beware of 20% risk of VUR in ‘normal’ kidney, advise parents to recognise UTI/pyelonephritis (especially if fever is without obvious focus)
• MCUG or prophylaxis until continent ONLY if dilated pelvis or ureter in good kidney 
• Annual blood pressure check until kidney involuted
• If cysts persist >5 yr, enlarge or hypertension, refer to urology

Ureterocoele (often occurs with duplex kidney)

• MCUG (if VUR or PUV suspected)
• MAG3 to check function and drainage from both moieties of the duplex system
• Prophylaxis until problem resolved
• Urology referral – sooner if obstruction suspected

Solitary kidney/unilateral renal agenesis

• Kidney ultrasound at 6 weeks to confirm antenatal findings and rule out other urogenital structure abnormalities
• DMSA to confirm absence of 1 kidney + normal uptake pattern by the single kidney

Renal parenchymal problem requiring nephrology review

• Bright kidneys
• Multiple cysts

Other conditions

• Single umbilical artery in cord

  • increased risk of renal abnormality but postnatal ultrasound scan only if antenatal scan missed or abnormal

• Ear abnormalities: ultrasound examination only if associated with:

  • syndrome

  • other malformations

  • maternal/gestational diabetes

  • family history of deafness