If you wear a removable retainer it will be impossible to expand. Let's just say you expand a little bit, when you wear the removable retainer, presumably for the night, the teeth will shift back.

and with fixed retainers

@sinned

I see..so I won't get any expansion wearing my retainer. But will the maxilla come forward at least? (Given that I wear the retainer at night and mew throughout the day)

@andre

Sure, but remember that expansion is associated with upswing, by that I mean that as you gain expansion tongue posture becomes easier therefore creating more expansion and upswing. It's possible that you can get upswing without expansion but you obviously want expansion as well, plus it might be a bad idea to mew while also wearing an expander, at least for the long term, with the teeth shifting back and forth root resorption might occur.