Pyelectasis is a ilation of the renal pelvis. The term is derived from the prefix pyelo- meaning "pelvis" and ectasia meaning "dilation or distension". It is a relatively common ultrasound finding and is three times more common in male fetuses. In most cases pyelectasis resolves normally, having no ill effects on the baby. The significance of pyelectasis in fetuses is not clear. It was thought to be a marker for obstruction, which in some cases it can be. In most cases it resolves spontaneously. In some studies it has been shown to appear and disappear several times throughout the course of pregnancy. There is some discussion about what degree of pyelectasis is considered severe enough to warrant further investigation and most authorities use 6mm as the cut-off point.