I'm pretty sure there's loads of threads on this but I'm too lazy to sift through! I want to get a birth ball if possible but am worried about the sturdyness of them considering I'll be heavily pregnant! How much weight do they take?
You need to be sure it is burst proof. Reebok ones (Reebok gym ball, £8, Argos) are, cheaper ones aren't. Reebok ones comes with a widget to let you blow it up with a bike pump,
They need to be big enough that your knees are about level with your hips when you sit on it. I am 5'8" and have a 65 cm one. Much taller, and you'll want a 75 cm one, much less that 5'6" you'll want a 55 cm one.
Birth balls, pilates balls and gym balls are all exactly the same thing, but those marketed as gym balls much cheaper!