With my second pregnancy, my 20 week u/s showed an enlarged kidney. I was told that there was nothing they could do in-utero except watch the development, so they could be prepared if anything was needed after birth. Best case, it would correct itself, worst case, kidney transplant. I was sent for another scan at 30weeks. This time I was told the kidney was fine but that the ureter was dilated (the duct leading to the kidney). Best case, it would correct itself, worst case, a life of being prone to UTI and bladder infections. I continued my pregnancy and delivered a healthy baby boy. He was put on a very small dose of preventative antibiotics for 6 weeks. At that time I took him for an ultrasound and a dye contrast procedure. The u/s showed that there was an abnormality to his kidney, but the ureter was fine. The second test showed that he had what they described as a skin flap on his kidney, which was why it was showing up "enlarged/abnormal" on the scans. But he had no reflux back in to the kidney which was the main concern. He was taken off antibiotics and we were told to bring him back at a year for another u/s. At one year of age the flap was almost gone, and at 2yo there was no sign of it. My son is almost 5 now and has never had any uti/bladder/kidney issues to date.
As hard as it is to hear something could be wrong, it is helpful to know if specialists will be needed at delivery. Hopefully your grandbaby will grow and develop out of this condition like my son did. Best wishes to all!