the baby and its heart beat can be detected relatively easily with trans-abdominal and trans-vaginal examination.
This is presuming that the pregnancy is actually at this stage of development.
For transvaginal ultrasound you can have an empty bladder Dating scans are usually recommended if there is doubt about the validity of the last menstrual period.
For example if you a tiny sac can be seen in the uterus, but the baby and its heart beat may not be detected yet.
Most dating scans are done with a trans-abdominal transducer and a fullish bladder.