Abstract:ObjectiveTo analyze the changes,outcomes and prognosis of dilatation or separation of the fetal renal collecting system at different gestational ages.MethodsFrom the women in mid to late pregnancy,312 kidneys of dilated renal collecting system were screened and grouped according to the degree of renal calyx dilatation,the value of anteroposterior diameter (APD) of renal and renal parenchymal thickness.From fetal to postnatal stages,the changes and outcomes of hydronephrosis were observed during three follow-up times.ResultsThere was no progressive aggravation or normalization of renal pelvis separation in 220 kidneys before and 4 months after birth.In 64 cases of undergoing surgical treatment within 1 year after birth,there were 30 cases of congenital ureteropelvic junction obstruction,14 cases of duplicate kidney,10 cases of congenital megaureter,8 cases of upper third ureteral stenosis and 2 cases of ureteral cyst.The renal function of the affected side was good after operation in the infants operated between 4 months and 2 years after birth.No significant increase in hydronephrosis was found in 28 kidneys without surgical procedure,and the renal function was normal during the observation period.ConclusionsIt is more objective to evaluate the degree of hydronephrosis with fetal pelvicalyceal dilatation combined with APD value and renal parenchymal thickness.In most cases,the fetal renal pelvis separation can return to normal before and after birth.The infants with moderate and severe hydronephrosis should be closely followed up,and early surgical treatment after birth has a good prognosis.