Urinary tract dilatation classification

Last revised by Dr Daniel J Bell on 22 Apr 2021

The urinary tract dilatation (UTD) classification system is a proposed unified classification of urinary tract dilatation for prenatal and postnatal care. This classification was formed with the collaborations from eight societies (American College of Radiology (ACR), American Institute of Ultrasound in Medicine (AIUM), American Society of Pediatric Nephrology (ASPN), Society for Fetal Urology (SFU), Society for Maternal-Fetal Medicine (SMFM), Society for Pediatric Urology (SPU), Society for Pediatric Radiology (SPR), and the Society of Radiologists in Ultrasound (SRU)) 1.

Classification

The UTD classification system uses six ultrasound findings to describe the urinary tracts:

  • anterior-posterior renal pelvic diameter (APRPD)
  • calyceal dilation with distinction between central and peripheral calyces postnatally
  • renal parenchymal thickness 
  • renal parenchymal appearance
  • bladder abnormalities 
  • ureteral abnormalities
Antenatal

Applicable after 16 weeks gestation:

UTD A1
  • anteroposterior renal pelvic diameter
    • 16 to 27 weeks: 4 mm to <7 mm
    • ≥ 28 weeks: 7 mm to <10 mm
  • with or without central calyceal dilatation
UTD A2-3
  • anteroposterior renal pelvic diameter
    • 16 to 27 weeks: ≥7 mm
    • ≥28 weeks: ≥10 mm
  • peripheral calyceal dilatation
  • abnormal parenchyma thickness or appearance
  • abnormal ureter or bladder
  • unexplained oligohydramnios
Postnatal

Applicable after 48 hours of life:

UTD P1 (low risk)
  • anteroposterior renal pelvic diameter 10 mm to <15 mm
  • central calyceal dilatation
UTD P2 (intermediate risk)
  • anteroposterior renal pelvic diameter ≥15 mm
  • peripheral calyceal dilatation
  • abnormal ureter
UTD P3 (high risk)
  • anteroposterior renal pelvic diameter ≥15 mm
  • peripheral calyceal dilatation
  • abnormal parenchymal thickness or appearance
  • abnormal ureter
  • abnormal bladder

See also

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