but from what I have read, it seems the prematurity plays into the lost IQ points (on average) more than the fact of being twins. Also, too many twin pregnancies have ended tragically on the pink board. AngMc and I have 25 weekers but we are very much the lucky ones.
Like I said recently, take a good hard look at the avg number of embryos transferred per FET at your clinic, the success rates, and the twin rate. There is a fair bit to be extrapolated from those numbers in relation to one another.