Not only do you not need to, but you shouldn't! Too many racers shift for the speed they will be going, rather than the speed they are going. This would be like pulling onto an on-ramp in your car, and shifting into 6th to accelerate up to highway speed.

In competition, sprints should start at the high end of a "normal" cadence. If you train yourself to develop power even at just 125 rpm, then you can start a sprint from 32mph at 100rpm, and accelerate to 40mph without shifting.