The model was spotted Tuesday for the first time since it was revealed she's expecting a child with her jiu-jitsu instructor boyfriend Joaquim Valente ... hitting up a Pilates class in Miami.

Gisele is doing a pretty good job hiding her baby bump here ... mostly shielding her stomach from prying eyes with a large bag, a baggy overshirt and black tights.

Despite the cover-up, we do know Gisele is over halfway through her pregnancy ... as we first reported, she's around 5 or 6 months pregnant.

Gisele's going to be a mother again at 44, and we've always seen her being super active with Joaquim ... and it appears she's sticking to her routine.

The pregnancy came as a shock to some, but as we've told you ... Gisele gave her ex-husband Tom Brady and their two kids a heads-up before the media found out.

Still, Tom seemed to comment on Gisele's pregnancy ... or at least react to it ... with a cryptic social media post after the cat finally came out of the bag.