The inability, on examination of the external genitalia of a newborn, to unequivocally assign the sex of rearing is a medical emergency. When this congenital anomaly occurs, rapid gender assignment is urgent. It will profoundly affect the success of the outcome for the child and family regardless of the cause of the ambiguity. Rapid assignment of gender may be accomplished by combining the findings of the physical examination with the detection of a uterus by ultrasonography.
Newborns with palpable gonad(s) in the inguinal, labia major, or scrotal areas and a uterus detected by ultrasonography should be assigned the female gender, regardless of phallic size. These newborns have a Y chromosome deletion or defects in the testis-determining factor of the Y chromosome and/or translocation of the testis-determining factor to the pseudoautosomal region of one of the X chromosomes. In the former case, newborns have a 45,X/46,XY karyotype and asymmetric gonadal dysgenesis.