Hello. This is related to antenatal hydronephrosis In which AP diameter of renal pelvis is very important. The vast majority of cases (~96%) with mild pyelectasis in the second trimester resolve, either during pregnancy or in the early postpartum period. The risk of postnatal renal pathology is increased with: increasing degree of pelvic dilatation in utero progression bilateral involvement Antenatally detected renal pelvic dilatation, especially in isolation, is considered a weak predictor of vesicoureteric reflux although postnatal sonographic evaluation is often recommended. Hope this helped you.