Have you thought about using a birth ball (also called a gym ball) during pregnancy, labour, and even after birth? These simple, inexpensive balls can make a huge difference in helping you stay comfortable, support your body, and work with your baby. Here’s everything you need to know about choosing, using, and loving your birth ball. Choosing the Right Ball Size matters. The diameter of the ball should match your height: 5ft 4” or shorter → 55cm ball Up to 5ft 8” → 65cm ball