Abstract： Objective To study the antenatal diagnosis and clinical outcomes of fetal pyelectasis to provide evidence for prenatal counseling.Methods The anteroposterior diameter(APD) of the pelvis was measured when fetal pyelectasis was detected during prenatal sonography and all pyelectasis cases were divided into mild,moderate and severe group.All cases were followed up and some received karyotyping.Results Totally,128 fetuses were identified with different degrees of pyelectasis.Twenty-eight out of the 128 pregnancies were terminated among which 24 complicated with fetal anomalies and 7 were identified with chromosome abnormalities.The rest 100 pregnancies were continued,including 86 sides of fetal pyelectasis in the mild group,39 in the moderate group and 30 in the severe group.The spontaneous regression rate in the three groups was 96.5%(83/86),61.5%(24/39) and 3.3%(1/30) respectively and 20.5%(8/39) of those in the moderate group and 73.3%(22/30) of the severe group underwent operation after birth.The regression rates of fetal pyelectasis decreased with the increase of the severity of fetal pyelectasis(x2= 88.730,P<0.01).The proportion of operation was positively correlated to the degree of fetal pyelectasis (x2= 2.045,P<0.01).Among the 69 fetuses who received karyotyping,7 (10.1%) were abnormal.Conclusions Most of the mild and moderate fetal pyelectasis regress spontaneously.However,the risk of chromosome abnormality is increased when such fetuses complicated with other deformities,thus karyotyping is necessary.Those with moderate and severe pyelectasis are likely to have abnormalities of urinary or other systems.