Fluctuating fetal or neonatal renal pelvis: marker of high-grade vesicoureteral reflux.

Fetal renal pelvic dilatation is a predictor of vesicoureteral reflux (VUR), but has low specificity. The aim of this study was to determine the clinical significance of fluctuating size of the renal pelvis on sonography, particularly in relationship to VUR. We prospectively recorded fetal renal pelvic diameter >/=4 mm in 1,092 fetuses (692 boys), from May 1989 to December 1995, with a minimum follow-up of 7 years. Fluctuation, defined as size of renal pelvis changing by more than 4 mm during the course of obstetric (23), postnatal (128), and both pre- and postnatal (7) renal sonograms, was recorded prospectively in 159 (117 boys). Of the 1,092, 849 (593 boys) had a voiding cystourethrogram at a mean age of 7 weeks (range 3-20 weeks). Of the 31 (16 girls) with high-grade VUR, fluctuation was observed in 20 (9 girls). Fluctuation was strongly associated with high-grade VUR (odds ratio 11.1, P=0.0000003) and with renal damage (sensitivity 61%, positive predictive value 31%). Primary high-grade VUR was persistent, seen equally in boys and girls, and required surgery in the majority. Fluctuation was associated with renal duplication anomalies ( P=0.00009) and megaureter ( P<0.00000001). Fluctuation of the renal pelvis on sonography is a marker for persistent high-grade VUR and renal damage in girls and boys.