Background: Recent widespread use of ultrasound has led to new efforts at screening for congenital kidney and urinary tract abnormalities. However, a standard screening methodology, criteria defining abnormalities, and follow‐up procedures remain to be established. In order to establish screening criteria for these abnormalities, we performed a preliminary study in 800 1‐month‐old infants using provisional methods and criteria.

Methods: Based on the results of preliminary study, we screened 2700 1‐month‐old infants in a prospective study using the criteria of renal size (longitudinal diameter ≤35 mm or ≥60 mm, or a difference between sides of ≥10 mm), and of pelvic dilatation (Society for Fetal Urology [SFU] grade 2 or higher) as positive at the first ultrasound screening. We used the SFU grading system instead of anteroposterior pelvic diameter measurements for pelvic dilatation.

Results: One hundred and twelve (4.1%) of the 2700 infants had abnormalities at the first ultrasound screening, while 18 (0.67%) had congenital kidney and urinary tract abnormalities on further examination. Use of the SFU grading system enabled us to reduce the false‐positive rate at first screening, while maintaining a high diagnostic rate. The abnormalities consisted of ureteropelvic junction obstruction in seven infants, megaureter in two, hypoplastic kidney in four, vesicoureteral reflux in six (three were accompanied by hypoplastic kidneys or multicystic dysplastic kidney), multicystic dysplastic kidney in one, and horseshoe kidney in one.

Conclusion: These results indicate that our screening methods and criteria are useful variables for detecting congenital kidney and urinary tract abnormalities.