Exercising on a birthing ball in pregnancy can help to reduce any back pain you are experiencing and make it easier for you to move around. It can also help ease labour pain, reduce the pain of contractions (especially if you use it for a couple of months before you give birth), decrease anxiety and shorten the first stage of labour.
Using a birthing ball can also help you adopt different upright positions, which can help you to labour effectively. It may even shorten your labour by an hour or so.
If you have any health related questions I suggest you consult with a physician or health and fitness expert before attempting any of the exercises that are illustrated in this video. You understand that physical exercise can be strenuous and can expose you to the risk of serious injury. I urge you to obtain a physical examination from a doctor before participating in any exercise activity.