Mare preg with identical twins PGd but still scanned in foal?

as some will remember from previous question my mare was scanned in foal with twins. they are identical twin in the same sack so impossible to abort just 1. she had 2 shots of pg and has since been re scanned to see if she lost them. they are both still there. one is happy and healthy but the other is starting to look abit dodgy (vets words not mine lol). as the dodgy one still has heartbeat iv opted to re try the PG followed by another scan in 10 days to check if they still there. im kinda prayin for a miracle in that the dodgy one will be reduced but the healthy one stays, as they in same sack its pretty unlikely that one will survive the death of the other. i didnt want to risk leavin her for a few weeks to see if dodgy one reduced itself cos obviously the longer the preg the harder it is to abort. its already becoming difficult due to the fact shes developed endometrial cups so i really cant risk losing more time. how many PG shots does it normally take to abort a mare? she is now aroung 55-60 days