Multiple pregnancies are often in In Vitro Fertilization (IVF) procedure. Multiple pregnancies comprises of twins, and triplets. They are known as high order multiples when they are more than 2 or 3 babies. You can increase the chances of multiple pregnancies by deciding the number of embryos you want to transfer.
I also had a similar query few years back. When I asked my doctor, he said that this is quite common with IVF. I was fine with it but I was scared that if I had triplets how would I deal with it. But fortunately I had twins. So, make sure you discuss with your doc before you start with IVF procedure.