Sara,
Have you thought about whether you would like to put 2 embryos back if you have them?
We also used PGD to screen for a dominant gene, and my Dr felt strongly that if there were 2 good embryos they should both go back in, since the process of getting them was so expensive and trying.

He did get me to see an obstetrician who specialises in twins first, to make sure that I could handle a twin pregnancy without excessive additional risks.