The procedure is called PGD, or preimplantation genetic diagnosis. It is where they genetically screen your embryos for a disease (like CF) and choose the embryos without it.
I'm not sure if you can donate the embryos that are not used, but I would check with the reproductive lab when you go.
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Leah 26 w/CF, RN, 11 weeks pregnant, mom
<img src="http://i222.photobucket.com/albums/dd53/rubyroselee/Xmas07-MarieKens-LeahLandon.jpg">