With the advent of widespread sonographic fetal imaging, the detection of possible anomalies of the urinary tract has presented the pediatrician with the dilemma of managing the postnatal diagnostic workup.

A prenatal ultrasound may identify a dilated renal pelvis (pelviectasis). Often, the imaging report uses the term hydronephrosis rather than pelviectasis. The fetal renal pelvis is detectable when a level 2 prenatal ultrasound is done between 18 and 22 weeks of gestation. Antenatal hydronephrosis (ANH) is based on the maximum anteroposterior diameter (APD) of the pelvis estimated on a transverse ultrasound image of the kidney. If the APD is 5 mm or greater, ultrasound surveillance of the fetal kidney continues with serial follow-up imaging through the third trimester.

ANH is variously reported as occurring in approximately 1%-2% of pregnancies. One report found it in 7.7% of prenatal fetal sonograms at 28 weeks of gestation, but it did not persist in...

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