Step aerobics is not the best as it involves repetitive strain on the same impact points.

A good low impact aerobics instructor will vary the steps so that you do some on the spot toe to heel and some walking forward which is heal to toe, some side steps and other variety of steps so that no one area is overly strained. This is generally not achievable in step aerobics so the same parts of the foot are under constant impact. It is also quite a strain on the knees. Stepaerobics is ok for most people although perhaps not too many sessions a week, but should preferably be avoided during pregnancy.

Zoot