To analyze the values of anteroposterior diameter (APD) in fetal renal pelvis separation during different gestational weeks and in predicting the prognosis.

Totally 182 cases of fetal renal pelvis separation in the Second Affiliated Hospital of Soochow University were enrolled in this study between January 2013 and October 2015. All of them were followed up to 12 months after birth. The detecting gestational weeks of non-reversible renal hydronephrosis and values of fetal renal pelvis APD were analyzed.

Among the 182 cases of fetal renal separation, 46 cases were detected in the second trimester, 136 cases were detected in the third trimester (bilateral renal pelvis separation occurred in 92 cases). During the follow-up, 114 cases recovered in the fetal period and 52 cases recovered within 12 months after birth, finally, 16 cases (8.8%, 16/182) of them progressed to non-reversible renal hydronephrosis. Among the 16 fetus of non-reversible renal hydronephrosis, 10 cases (62.5%, 10/16) were detected in the second trimester, their values of APD were 7.4-11.5 mm and the average was (8.0±1.5) mm; 6 cases (37.5%, 6/16) were detected in the third trimester, their values of APD were 13.6-14.8 mm and the average was (12.8±2.0) mm. The values of APD in fetus who were detected in the second trimester were smaller than those in the fetus who detected in the third trimester and the prognosis in the fetus who were detected in the second trimester was worse than those in the fetus who were detected in the third trimester, the fetus (21.7%, 10/46) who progressed to non-reversible renal hydronephrosis in the second trimester were more than the fetus (4.4%, 6/136) who were detected in the third trimester.

Clinical following-up combined with the detecting gestational weeks of fetal renal pelvis separation and values of fetal renal plevis APD by prenatal ultrasound may be helpful in predicting their prognosis.