My son is now 11 months old. I didn't have any other testing done, but the u/s at 20 weeks showed that his kidneys were enlarged. I want to say 4mm? They did a repeat u/s at 26 weeks and the same thing. They weren't worried because he had sufficient amniotic fluid. I did some research then and found that dilated kidneys were quite common and it usually went away before birth or just after. The Dr did tell me that the dilated kidneys increased my chances of having a baby w/ DS by 1%. I wasn't worried because there weren't any other signs.
At 36 weeks we had another u/s b/c the stress test performed earlier that morning didn't show sufficient movement. The u/s showed very enlarged kidneys and low amniotic fluid. The dr took my son by emergency c-section just a few hours later.
Nicholas, my son, has a lot of health problems. I am not telling you this to make you worry, but to let you know that even after all is said and done, we are still here!! When Nicholas was 4 days old we were given a 50% chance that he'd make it to his first b-day because of all of his issues (not just the kidneys)....and here we are approaching it very quickly! (Too quickly!!) He is doing fine...all things considered. He had post urethral valve. That is where a blockage is formed by a flap of skin (or some obstruction) that prevents the bladder from draining w/ out a lot of pressure. The urine gets backed up (or refluxes too) and when that happens for a long time, it causes damage to the whole urinary tract. He had the blockage removed around 2 1/2 weeks of age and pees just fine now!
Because of the damage to his kidneys, he will eventually need to have dialysis and a kidney transplant, but that should be a long while yet. The post urethral valve is not DS specific. Our pediatrician's office said that they have 4 kids now that had that when they were born....and I think Nicholas is the only kiddo who has DS.