In utero progression of isolated renal pelvis dilation.

The objective of this study to determine the risk of in uteroprogression of renal pelvis dilation when detected on antenatal ultrasound examination. We reviewed 230 fetuses with evidence of renal pelvis dilation. At least one exam was subsequently performed prior to delivery in all cases. Renal pelvis dilation was defined as an anterior-posterior renal pelvis measurement > 4 mm at < 32 weeks' and > 7 mm at > or = 32 weeks' gestation. Hydronephrosis was considered to be present when the renal pelvis measured +10 mm independent of gestational age. Multiple gestations and fetuses with additional congenital anomalies were excluded. The mean gestational age at diagnosis was 24 weeks. Renal pelvis dilation progressed to hydronephrosis in a total of 10.9% (25 of 230) of fetuses. There was a 3.3% chance of unilateral renal pelvis dilation progressing to hydronephrosis versus 26.0% in bilateral dilation (OR 10.4 [95% Cl 3.5-33.3]). Of those fetuses with progression, 80% had bilateral dilation (p < 0.0001). There was no difference in progression between right and left kidneys. Additionally, gender, gestational age at diagnosis and delivery, and birth weight did not differ between those fetuses with and without progression. The hydronephrosis in 7 of 25 (28%) regressed to pyelectasis on a subsequent ultrasound exam. Thus, the overall rate of progression of renal pelvis dilation to persistent hydronephrosis was 7.8% (18 of 230). In conclusion, the risk of isolated renal pelvis dilation progressing to hydronephrosis is low. Although bilateral pelvis dilation carries a higher risk for progression, no fetus in our study required in utero intervention. A follow up scan prior to delivery may be considered to identify those fetuses who will require postpartum intervention.