mizzsocial,

Don't know if this info is helpful but it sure was to me.

The renal pelvis is a part of the kidneys that collects urine as it is being produced, before transporting it down the ureters and into the bladder. When an ultrasonographer routinely checks an unborn baby's kidneys, they may notice that the width of the renal pelvis in one (or both) kidneys is more enlarged than expected. This is referred to as 'renal pelvis dilatation' (or RPD). It is believed that about 2% of women will be told that their unborn baby has some degree of RPD.

The dilemma of detecting any degree of renal pelvis dilatation is that in most cases (up to 84%) the baby does not have a health problem and the RPD generally rights itself by the time the baby is one year old, without being harmful to them or requiring any medical treatments. The reason for this is that some babies are genetically predisposed to taking longer to mature their urine collecting system.
Is this Dilated Renal pelvis what you were diadnosed with?

Hope you are not stressing out too much. Have you seen you ob since the u/s. They can explain it a lot more.