The mother of a 4-year-old girl came to an endocrinologist with complaints about the abnormal structure of the child's external genitalia: hypertrophy of the clitoris and an enlarged fabia that resembles a scrotum, Additionally, the child exhibits accelerated growth, as well as growth of axillary and pubic hair, and lowering of the vocal timbre. What examination is necessary to confirm the diagnosis in this case?