Occasionally, if they can't see what they need to, the sonographer may ask you to have a transvaginal scan, where a very thin probe is used to look at the baby from close to the cervix. You will be able to watch the monitor and see the first pictures of your baby, which is always an extraordinary moment, whether this is your first baby or your fifth.It may not be immediately obvious which parts of your baby you're looking at, but the sonographer will be able to help you work it out.They will look at the placenta itself and will take note of its position, which may have implications for later in the pregnancy.A low-lying placenta usually moves up later in the pregnancy but if it doesn't, it can cause problems in labour so they will want to check its movements throughout your pregnancy.This will give you a more precise estimated due date.Are you expecting just one baby, or could it be twins or (gulp) even more?You might feel a bit of pressure but it doesn't actually hurt and won't harm your baby.
You will have had earlier appointments and may have had an early scan if you've had any concerns such as bleeding, but otherwise this is the first time you'll get to see your baby, so it's a real milestone in your pregnancy.
He or she may need to prod your belly a bit to “encourage” the baby into a suitable position.
After a long first trimester, when you might well have had worries, or even wondered if there can really be a baby in there, it is a great comfort and a huge relief to see your baby on the screen and have the reassurance that everything is OK in there.
It's not completely foolproof – but the dating scan is a much more accurate way to work out how far you are into pregnancy than calculating it by the date of your last period, which is the only method the midwives will have used so far to work out your due date.
You may find at this scan your due date is altered on your notes.