Hi Joy - when pregnant one has to be extra careful and aware in any physical practice and yoga is no exception, although it can dramatically improve and aid in both the pregnancy and birthing. I generally don't suggest starting a vigorous form of yoga when you are pregnant but if you can find a gentle and comfortably paced class in your area then go ahead. The best option would be a specific prenatal class for pregnant mothers. I don't know of any teachers in Nelspruit but try the local classifieds or maybe a health store to try and initiate yourself in what could be a life changing practice.
Good luck.
Chris