Abstract: Dilation of the fetal renal collecting system，antenatal hydronephrosis，is one of the most common abnormalities detected on prenatal ultrasonography（US）， reported in approximately 1%-5% of all pregnancies. Some fetal
hydronephrosis can always spontaneously disappear after birth， which is called physiological hydronephrosis，and some may deteriorate and cause renal function damage，which is called pathological hydronephrosis. There was little literature to report how to differentiate fetal physiological and pathological hydronephrosis. The degree of hydronephrosis classified by antero-posterior diameter（APD） characterized the antenatal hydronephrosis data across most of the studies. Some people also prefered to diagnose hydronephrosis by other ultrasound findings，such as renal calycealdilation，renal echogenicity，parenchymal thinning，bladder dilation，amniotic fluid level and so on. There is no consensus on the diagnosis and classification of fetal hydronephrosis. We summarized some new ultrasonic diagnosis indices，so it could provid evidences of evidence-based medicine for docters to deal antenatal hydronephrosis.

Key words: Ultrasonography, Fetal diseases, Fetal monitoring, Hydronephrosis