Talk to Pediatrician on Karyotyping

My son is 3 weeks old. He has problem of undescended left testis while right testis was not seen in ultrasound. Doctor has suggested that karyotyping to know the gender. He has proper male genital organs, but penis size is relatively small with thick layer of fat outside. I want to know is there any chances that he may not be male child?? Whether I should go for karyotyping or not as this test is bit exoensive