Urinary tract dilatation classification

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

​In 2021, Nguyen et al. updated and clarified the classification system, drawing on the experience gathered from the use of the 2014 classification ⁴​. The following is based on the update:

Classification

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

• anterior-posterior renal pelvic diameter (APRPD)​

• calyceal dilatation, with distinction between central and peripheral calyces postnatally

• renal parenchymal thickness, either normal or abnormal

• renal parenchymal echogenicity, either normal or abnormal 

• bladder abnormalities, either present or not

• ureteral abnormalities, either present or not

Antenatal

UTD A1

• anteroposterior renal pelvic diameter

  • <28 weeks: 4 mm to <7 mm

  • ≥28 weeks: 7 mm to <10 mm

UTD A2-3

Any of the following:

• anteroposterior renal pelvic diameter

  • <28 weeks: ≥7 mm

  • ≥28 weeks: ≥10 mm

• any calyceal dilatation, with APRPD ≥4 mm or calyceal dilatation 

• any ureteric dilatation, with APRPD ≥4 mm or calyceal dilatation

• parenchymal abnormality, bladder abnormality, or oligohydramnios

Postnatal

Applicable after 48 hours of life:

UTD P1 (low risk)

Any of the following: 

• anteroposterior renal pelvic diameter 10 mm to <15 mm

• central calyceal dilatation

UTD P2 (intermediate risk)

Any of the following: 

• anteroposterior renal pelvic diameter ≥15 mm

• peripheral calyceal dilatation

• ureteric dilatation ≥4 mm, with APRPD ≥10 mm or calyceal dilatation 

UTD P3 (high risk)

Parenchymal abnormality, bladder abnormality, or oligohydramnios, plus any of the following:

• anteroposterior renal pelvic diameter ≥15 mm

• any calyceal dilatation

See also

• hydronephrosis grading (SFU)

• fetal hydronephrosis

• fetal pyelectasis

• neonatal hydronephrosis