Hi, I have gone through your question. Minimal dilatation of renal pelvis in the fetus has to be thoroughly investigated. It is one of the sonographic marker of Downs syndrome and hence other markers like short nasal bone, echogenic intracardiac foci, ventriculomegaly etc have to be looked for in proper ultrasonographic examination. If others are also found, you need to consult a fetal medicine specialist, so that prenatal chromosomal analysis of your baby can be done by either amniocentesis or cordocentesis. Other causes of unilateral renal dilatation are kidney anomalies which are usually present on one side and are not very harmful. Such babies need to be followed up with repeated ultrasounds with advancing pregnancy to see for increasing dilatation, and a repeat ultrasound and renal X-rays on birth. Hope you found this answer helpful. Wishing you good health.