Popular use of fetal ultrasonography has increased to detect congenital hydronephrosis(CH) which is the most common anomaly prenatally detected. We'd like to determine the frequency and clinical characteristics of prenatally diagnosed CH and outcome of ureteropelvic junction stenosis(UPJS).

The records of births between January 1994 and June 2003 in Chonnam National University Hospital(CNUH), and the records of children who were diagnosed with CH in the Department of Pediatrics of CNUH during the above period, were retrospectively analyzed. In the patients with UPJS, the initial anterior posterior diameters of renal pelvis(APD) were compared between the spontaneous regression(SR) and operation group(OP). In the SR group, sequential regression rates of APD were estimated.

Among a total 9,076 births, 231(2.54 percent) patients with 293 renal units were diagnosed as CH and 19(6.78 percent) renal units spontaneously regressed 3 days after birth. In 228 children(56 bilateral; 172 unilateral; total 284 renal units) diagnosed with CH in the department of pediatrics of CNUH, male(71.9 percent) and left kidney(69.2 percent) predilection were found and 78.1 percent of CH were caused by UPJS. The initial APD of the SR group(121 units) in UPJS was 7.8±6.28 mm, which was significantly smaller than the APD(26.8±12.14 mm) of the OP group(25 unit) ( P <0.05). In the SR group, 81 percent spontaneously regressed within one year.

In CH, male and left kidney predilection were found. UPJS was the most common cause of CH and initial APD in UPJS at 3 days of age was a good prognostic indicator. Close monitoring should be done for at least one year because most SR in UPJS regressed spontaneously within one year.