Ultrasounds performed during the first 12 weeks of pregnancy are generally within 3 - 5 days of accuracy.
The most accurate time is between 8 and 11 weeks gestation.
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.
The dating scan is non-intrusive and won’t be painful; in fact, it can be quite a relaxing and exciting experience to see your little one and their tiny heartbeat for the first time.
Your sonographer will be able to answer any questions you have on the day and will talk you through the process.The sonographer will then use a transducer device which uses ultrasound to produce an image of your baby inside the womb to a small display screen next to you. The dating scan is the first time you (or anyone) will have seen your baby so there’s a few things that your sonographer will look out for and things you’ll find out: • How many weeks pregnant you are, and your EDD (estimated date of delivery).This will be a lot more accurate than working it out just using the date of your last period.Most dating scans are done with a trans-abdominal transducer and a fullish bladder.If the pregnancy is very early the gestation sac and fetus will not be big enough to see, so the transvaginal approach will give better pictures.