Measure the anteroposterior renal pelvic diameter on a transverse view and add calyceal dilation, parenchymal thickness and appearance, ureter, bladder and liquor — the UTD A1/A2-3 grade sets postnatal follow-up.
Orient first
- UTD consensus (2014) replaced "pyelectasis" grading (verify the thresholds used locally).
- Thresholds are gestation-specific: APRPD ≥ 4 mm before 28 weeks and ≥ 7 mm from 28 weeks.
- Bilateral dilation with a thick-walled bladder and a keyhole sign in a male fetus suggests posterior urethral valves.
Acquire the study
- Transabdominal ultrasound; transverse view of the fetal kidneys with the spine at 12 or 6 o'clock.
The manoeuvre
- Transverse view: anteroposterior renal pelvic diameter in mm at the inner edge of the pelvis.
- Calyceal dilation: central vs peripheral.
- Parenchyma: thickness, echogenicity, cysts.
- Ureter visible (dilated), bladder wall thickness and emptying, keyhole sign.
- Liquor volume (deepest pool or AFI) and gestational age.
What confirms it
- UTD category A1 or A2-3 stated with each component.
What licenses you to exclude it
- APRPD below the gestational threshold with no other abnormal component is normal.
The classic misread
- Measuring the pelvis on a sagittal or coronal view (overestimates).
- Ignoring liquor — oligohydramnios moves the case to the high-risk group.