I heard from my friend that at St Teresa, they will ask which doctor refers you first before they confirm that you have the option "not" to join package. That is to say, hospital allows prenancy women referred by a certain list of doctors the option of join or not to join package. If your doctor does not fall into that list, you don't have the choice but to join package.
My doctor always recommends us not to join package to save money at St Teresa.