Nobody should stay pregnant while on Xanax or/and Subutex, even Xanax itself is extremely dangerous for baby and her future development... what is clearly written on the label of medication.
Various birth deffect might occur, immediately visible or invisible in the beginning, like low immunity - too low to cope with infections, problem with development of heart, lungs, brain, various neural problems, hormonal problems, especially in puberty, emotional and psychological problems, very high possibility for child that one day he/she becomes addict to mind altering medications or drugs, especially if mother is continuing to use them ----list is very long, and question about possible side-effects should be always asked before pregnancy.
The truth is also that every baby is different, so you might be lucky and your baby might experience only few minor problems, that could be solved with various natural methods, with vitamins, minerals, healthy food and a lots of love and patience over the years.
I wish you that luck. But please, never gamble with pregnancy under any medication because you seriously gamble with the life and health of your future child on that way.