You probably know when your LMP was, but not when you actually conceived.
If you do know the conception date, this is counted as day 14, and not day one.
If your uterus (womb) is very deep in your pelvis, or if you're overweight, you may be offered a vaginal scan, which can get nearer to your baby.
It shouldn't be uncomfortable, and you don't need a full bladder.
Looking for abnormalities isn't the purpose of this scan, though.
That's the job of your next routine scan at about 20 weeks, when more detail can be seen as your baby grows bigger.
Not all units offer an early scan if all is going well in this pregnancy, though.
Ask your GP if you want the reassurance of an early scan. The scan's main purpose is to work out accurately how many weeks pregnant you are and estimate your due date.
For most mums-to-be, the first scan will be a dating scan at between 10 weeks and 13 weeks plus six days of pregnancy.
However, the timing of your first scan will also depend on how your pregnancy is going, and where you live.
Nearly all scans after 10 weeks can be done through your tummy, and most units ask you to come with a full bladder.
The sonographer will put some gel on your tummy and will move a small hand-held device (a transducer) over your skin to get views of your baby.
The dating scan will also show if you're expecting twins, triplets or more.