Actually, there aren’t any “midgets” any more- at least not in the States. It’s a condition that can be easily cured. Now, dwarfism, is another matter.
Midgets lack a proper amount of human growth hormone (HGH) (IIRC), because HGH is easily produced and administered, there is no reason for anyone (in the advanced world) to have to be a midget if they don’t want to be.
Dwarfism is caused (IIRC) by a defect in a bone elongation gene. This is not as easily produced and administered as a dwarf is born as a dwarf; while a midget just fails to develop proper human growth without the application of HGH (by nature or medical administration).