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It is problematic to have renal pelvis
dilation findings because they indicate some pathology in the fetus KUB. The child should be managed by a urologist/pediatric surgeon immediately after birth. There can be many causes for such problem like obstructing valves at the ureter
end, ureter opening atresia, straight opening of ureter leading to reflux of urine to name a few.
The child would most likely need a surgical intervention.
Please get these investigations and if you like, inform me in a Fresh Query / Follow up Query for further fine tuned opinion
Wish you a great health!