What are the benefits/disadvantages of prednisone vs. hydrocortisone to treat late-onset congenital adrenal hyperplasia? i want to become pregnant.

either one: Either one. Assuming your diagnosis is correct (you should be seeing an endocrinologist), the steroid needs to suppress adrenal androgens, normalize periods, etc. Prednisone lasts longer (take 1x/day), but it is easy to take too much. A frequent used regimen is hydrocort 3x/day. It can give better suppression of androgens. Your adrenals will get supressed, and you will need stress doses.