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What are 2D, 3D and 4D ultra sound scans?

A 2D scan is a still picture of your baby in two dimensions. The image is generally black, white and grey, a little blurry outline of a 2D image and is quite hard to decipher. This is because the scan sees through your baby so the photos show the baby’s internal organs.
A 3D scan is a still picture of your baby in three dimensions. It’s just like a photo.
A 4D scan is a moving version the 3D image of your baby.
A 2D scan is quite hard to decipher unless you have the help of a trained Sonographer who is the person that operates the ultrasound machine.
With a 3D scan, you can make out the baby’s shape, skin and parts that stick out such as their limbs, nose, tongue, mouth etc.   You may often be lucky enough to make out your baby’s face but this will depend on what position your baby is lying in on the day and how obliging they are if they are encouraged to move around to reposition themselves.
A 4D scan will give you all of the above under 3D but will have the added feature of movement.  This means for the duration of the scan you will be able to see your baby move and in many cases the scan provider will burn you a recording of the scan onto a DVD to view at home.  
In many cases, your 20 week scan will be done on a normal 2D machine.  If you decide to have a 4D scan, you will generally have to visit a private clinic and will be charged a fee.  The best time to book such a scan is between 26 and 31 weeks. 
From a medical perspective, the benefits of 3D and 4D scans are limited.  They might show more detail about an abnormality, such as soft- tissue anomaly e.g. cleft lip, as they show more detail from different angles. 
As with a normal 2D scan, 3D and 4D scans are safe and no harmful effects have been established.
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