In both media, when Animagi transform from beast to human, they are fully clothed. In the Prisoner of Azkaban film, we see Wormtail leave his clothes behind, as he transforms into a rat. What happened to them?
Pettigrew left his clothes behind. Maybe because of the stressing situation but it's also possible to transform the clothing into the animagus form. It depends on the wizards intentions and skills as described in this answer to a similar question.