I like using _stutter_ instead of _speech impediment_. I say something like, "before we start I wanted to let you know I stutter, so you may hear me pause or repeat words. If you have any questions or need me to repeat anything, feel free to let me know." or sometimes I'll spice it up a bit. I try to disclose with confidence, not premonition. I would take out the part about increasing during points of high emotion. They don't need details and can understand interviews can be difficult for anyone.