Male:female=2:1
Antenatal pyelectasis improves in 98% of patients with grades 1-2 hydronephrosis (anteroposterior pelvic diameter <12 mm). Severe hydronephrosis (grades 3-4, AP pelvic diameter >12 mm) has a more uncertain outcome.
One meta-analysis found that even moderate antenatal hydronephrosis had a considerable risk of postnatal pathology. Archives of Disease in Childhood 2007;92:357-361
No large RCT, so current practice is to give prophylaxis to high risk (ie AP diameter 15+ mm (or if evidence of damage).
Other risk factors:
For high risk, do early USS (not first 3/7 as false negative due to underfilling, but before 14/7) then if persistent, DMSA and refer nephrologist. For low risk (10-15mm) USS 6-8/52 plus if over 12mm, DMSA. Under 12mm, rpt @6/12.
?Test fetal urine to get more info eg growth factors, beta2 microglobulin
On examination, look for mass, abdo wall muscle.
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