It seems there is an obstruction in the PELVI-URETERIC JUNCTION (PUJ), which is basically the outlet from the
Kidney. In many cases, the obstruction may get spontaneously relieved after birth, but not in all cases.
It needs serial sonographic monitoring to establish that the Cortico-medullary differentiation is maintained.
Don't be worried, as in many cases it resolves on it's own , without any intervention.
However it's advised that you stay in touch with your Obstetrician and Pediatrician for monitoring so that if there is any complication , it can be managed effectively.