NSTs for Twins

How do you bill NSTs for Twins? Some information I am finding states that you should for an NST on each of the twins (59025 x 2 or 59025 x 1 and 59025-59 x 1)? I have also been instructed in the past to only bill a single unit for both (59025 x 1).

It seems a little much to bill for both when it simply requires a second wire be attached for the second fetus.

I would appreciate any thoughts and references you might have.

Thanks

Cory