When you initiate the go around you will indeed go below the MDA.
Well you shouldn't! The aircraft "allowance" (in the case of a continuous descent approach) should be added to the MDA - if not visual at this altitude then you go around.
If you procedures are such that you intend to fly level to the MAP you also should not descend below MDA without the required visual reference.
This has previously been extensively discussed on Pprune - suggest you do a search!