This is called the dating scan. It's used to see how far along in your pregnancy you are and check your baby's development. Your midwife or doctor will book you. I am booked in for a dating scan on Friday which will be 6w5d (or for better results glad I did as it put me a little at ease yes you can't hear the. i have my scan booked for the 4th so this Monday and I will be 6w+5. if your dates are out slightly potentially you could be too early to see.
Dating scans are usually recommended if there is doubt about the validity of the last menstrual period. For example if you do not know when the first day of your last period, or the likely day of conception was have had irregular periods have had an when did you have your dating scan cycle because you recently stopped the oral contraceptive pill, or you recently had a miscarriage, or you are breast-feeding had some implantation bleeding which can be been confused with your last period date What can be seen?
Sometimes a trans-vaginal examination shows that your pregnancy is less advanced than expected. The scan or my dates - which should I believe? The EDD from the early dating scan is used - if the last menstrual period is not known or is unreliable, or the dating scan differs from the last menstrual period dating by more than 5 days. These scans are only used to estimate the due date of your baby if this is all you have to go on.
If you have more than one ultrasound during your pregnancy, giving you 'multiple dates', then the earliest ultrasound estimate should be used, because it will be more accurate.