Hello Thanks for your query. Mild dilatation of the renal pelvis is common, and in most cases, spontaneously resolves itself as the pregnancy progresses. As the rest of the TIFFA is normal, chromosomal anomalies are ruled out. Please continue to have serial ultrasounds, and if the dilatation increases or persists till term, then you need to have detailed evaluation, and consultation with a pediatric surgeon, as the baby might require surgery after birth. All the best.