Don't do it too early unless there's problem with your pregnancy, because if you do it too early, you will need to do the vaginal one which is very uncomfortable, and you might bleed afterwards, which is even worse.
If you can wait longer, when the fetus is bigger and has heart beat, then you don't need to do the vaginal one, and can do the one on top of your belly
I haven't seen my doctor yet, I probably will deliver in Queensway hospital, since my doctor is working there. Btw, when should I hear the baby's heat beat? I'm so looking forward.