Please arrive with an empty bladder. There is no problem if you have a period and are bleeding on the day of the scan, it can still be performed. Throughout the examination you are covered up and the door is locked.
If for a particular reason you are unable to have a trans-vaginal scan, an abdominal scan can be performed. If this is the case you must drink 1½ pints of water by 1 hour before your appointment time, because a very full bladder is essential to demonstrate the uterus and ovaries clearly when the ultrasound transducer is passed over the lower abdomen.