Objective:To investigate the postnatal grading, surgical intervention and prognosis in fetal hydronephrosis.Methods:The clinical data of 243 children who were prenatally diagnosed with fetal hydronephrosis and first seen at Dalian Children′s Hospital after birth from November 2014 to November 2017 were retrospectively analyzed. All cases were followed up by routine ultrasound after birth and were assessed and graded according to the postnatal urinary tract dilation (UTD) system. The children with clinical indication for surgery underwent surgical treatment (operation group), and the children without clinical indication were closely followed up (non-operation group).Results:Among 243 children, 182 were male and 61 were female; the gestational age at first diagnosis was (27.5±3.2) weeks, and the maternal age was (29 ± 6) years; 212 cases were unilateral, and 31 cases were bilateral. The results of the first ultrasound examination result showed UTD low-risk was in 117 cases, medium-risk in 67 cases, high-risk in 59 cases. All the children were followed up from 14 to 50 months, with a mean of 26.4 months. During the follow-up period, 117 cases with UTD low-risk did not undergo surgical treatment; 62 cases of 67 with UTD medium-risk did not receive operation, and 5 were operated; while operation were performed on 56 cases of 59 with UTD high-risk, and 3 children with stable hydronephrosis were not treated surgically. The non-operation group had 182 cases, and operation group had 61 cases. The UTD high-risk rate and renal pelvis anteroposterior diameter of first ultrasound examination in operation group were significantly higher than those in non-operation group: 91.80% (56/61) vs. 1.65% (3/182) and 1.9 (1.6, 2.4) mm vs. 0.7 (0.3, 1.5) mm, the thickness of renal parenchyma was significantly lower than that in non-operation group: 3.0 (1.3, 4.1) mm vs. 6.0 (5.1, 7.2) mm, and there were statistical differences ( P<0.01 or <0.05). The result of follow-up in operation group showed that the renal pelvis anteroposterior diameter and the ratio of renal pelvis anteroposterior diameter to renal parenchyma thickness 1 year after operation were significantly lower than those before operation: (1.6 ± 0.7) cm vs. (3.5 ± 1.5) cm and 0.3 ± 0.2 vs. 1.1 ± 1.0, the thickness of renal parenchyma and differentiated renal function were significantly higher than those before operation: (5.8 ± 2.4) mm vs. (3.2 ± 3.1) mm and (45.4 ± 1.9)% vs. (39.5 ± 2.3)%, and there were statistical differences ( P<0.05). Conclusions:UTD grading system is required after birth. Children with hydronephrosis in UTD low-risk and most of the UTD medium-risk have relatively satisfactory prognosis. The hydronephrosis children with UTD high-risk should undergo early surgery if progressive worsening appears and decline in differentiated renal function is detected.