Abnormal fetal genitourinary system morphology Fetal lower urinary tract obstruction 2022-04-10T19:18:17Z An obstruction in the ureter leading to bladder outlet obstruction. Special criteria are used for lower urinary tract obstruction (LUTO) in the fetus. Prenatal LUTO has classically been suspected on the basis of three ultrasonographic findings: megacystis, dilated posterior urethra (known as the keyhole sign) and hydronephrosis.