Is it permissible for me to fast the days I missed in Ramadan now, knowing that I am ten weeks pregnant and have completed the treatment for "Prader-Willi syndrome" associated with hunger, and will this affect the fetus or cause the disease to recur?

It is obligatory for you to make up the days you missed from the two previous Ramadans. Delaying the make-up does not waive it, even if for years. The general rule is to make up Ramadan (definition) before the next one begins. If one delays the make-up without a valid excuse, then she must offer expiation along with the make-up for each day. As for the one with a valid excuse, she only needs to make up the days. If you fear for yourself or your pregnancy by making up the days now, there is no sin in postponing it until you are able. And there is no sin in breaking your fast in the upcoming Ramadan due to pregnancy, if you fear for it or for yourself.