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 > or = 4 mm before 33 and/or > 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 > or = 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 > or = 33 weeks yielded a sensitivity of 100% and a specificity of 18.7% and 47.8%, respectively. The median APD (range) at > or = 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 > or = 19 mm underwent surgery. CONCLUSION Women with ultrasonographically detected prenatal fetal pelvic dilatation of > or = 4 mm before 33 weeks and of > or = 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.