Choice of Hospital

Hi, had when to poly to confirmed my prenancy and had the doc to refer me to sengkang hospital for all future checkup and labour will be done at KKH. Now me & husb wants to reconsider another hospital like NUH or SGH. How do i go about to make the changes? Shld i just go to the NUH/SGH directly or must i go back to poly to change the referral? Or can i just procees the chk up at sengkang hospital and req them to put me to the other hospital? Sorry, its my first prenancy hence i had no idea what to do ?