I can only speak from personal experience ...
My OB/GYN said multiples are VERY possible with Clomid AND my advanced age. I was 39 when we were trying for baby #1.
My daughter Addison is a Clomid baby.
It was my second round of Clomid after trying on our own for 8 months.
The first US showed 3 sacs !

Triplets on my first pregnancy ! Holy CRAP!
The next US showed 2 sacs with "poles" ... 1 had a heartbeats at that point, which was early according to my OB/GYN. Ok ... I can handle 2 babies ... haha
The next US only had the one sac ... the one that had the heartbeat in US #2.
My doc said he was sceptical to call it triplets ... did make a note on the US of possible twins with the second US ... but ultimately Addison was all I carried. He said my body absorbed the other sacs.
Medical studies ... I don't know ...
But that is my story (the short version) ... hope it helped