Urinary tract dilation classification system for pediatric hydronephrosis

The Urinary Tract Dilation (UTD) Classification System describes the appearance of the urinary tract based on antenatal and postnatal presentation. The antenatal presentation (left column) is divided into normal, A1, and A2-3, and measurements between 16 and 27 weeks and ≥28 weeks gestation. A normal urinary tract is one with no urinary tract abnormalities and anterior posterior renal pelvic diameter (APRPD) measuring less than 4 mm between 16 and 27 weeks gestation and less than 7 mm ≥28 weeks gestation. A1 describes a normal urinary tract with 4 to <7 mm pelvic dilation at 16 to 27 weeks gestation or 7 to <10 mm ≥28 weeks gestation with or without central calyceal dilation. UTD A2-3 is for fetuses if there is APRPD ≥7 mm between 16 and 27 weeks gestation or ≥10 mm ≥28 weeks gestation, peripheral calyceal dilation, ureteral dilation, renal parenchymal, or bladder abnormalities. The postnatal presentation (right column) is divided into normal, P1, P2, and P3. Measurements are more reliable if taken 48 hours after birth or later. A normal urinary tract is one with no urinary tract abnormalities and APRPD <10 mm. P1 describes a normal urinary tract with APRPD 10 to <15 mm and/or central calyceal dilation. P2 describes APRPD ≥15 mm or peripheral calyceal dilation. P3 describes additional ureteral dilation, abnormal renal echogenicity or cysts, or bladder abnormalities regardless of APRPD measurement.