The impact of fetal renal pelvic diameter on postnatal outcome

Objectives To determine thresholds for the fetal renal pelvic anterior–posterior diameter (APD) predicting postnatal clinically relevant pelvicaliceal dilatation. Methods One hundred and forty-eight infants whose prenatal sonography had identified an isolated uni- or bilateral fetal APD of ≥4 mm before 33 and/or ≥7 mm after 33 weeks' gestational age were investigated postnatally. On the basis of postnatal ultrasound examination, these infants were grouped according to the Society for Fetal Urology Grading System: no pelvic dilatation (n = 38); only pelvic dilatation (n = 59); pelvicaliceal dilatation (n = 33); pelvicaliceal and ureter dilatation (n = 18). Results Fetal pyelectasis of 7 mm was 89.3% sensitive and 78.9% specific <33 weeks, and ≥33 weeks pyelectasis of 10 mm was 88.4% and 78.6% in predicting subsequent postnatal pelvicaliectasis, respectively. Using a threshold of 4 mm <33 weeks and 7 mm ≥33 weeks yielded a sensitivity of 100% and a specificity of 18.7% and 47.8%, respectively. The median APD (range) at ≥33 weeks was 19 mm (9–36 mm) in patients requiring surgery and 13 mm (7–21 mm) in conservatively treated patients (p = 0.001). Thirteen of fourteen patients with APD ≥ 19 mm underwent surgery. Conclusion Women with ultrasonographically detected prenatal fetal pelvic dilatation of ≥4 mm before 33 weeks and of ≥7 mm from 33 weeks onwards of gestation should have repeated prenatal ultrasound scans and a detailed postnatal evaluation. The dilatations of an APD >4 mm before 33 weeks, which have disappeared at the post-33-week scan need no further investigation in the postnatal period. Copyright © 2004 John Wiley & Sons, Ltd.