3D ultrasound scans are still colour pictures of your baby in three dimensions. 4D ultrasound scans on the other hand are moving 3D images of your baby, with time being the fourth dimension.
In other words, 3D scans are similar to the coloured photos you see in newspapers and magazines. A 4D scan will be mostly recorded on a DVD and given to you.
Every mum is eager to have the first look at her child, and you will be looking forward to your first scan. However, the grey blurry outline of a normal 2D scan might have disappointed you. A two-dimensional scan sees right through your baby. This means that the photos you see show your baby's internal organs.
But this is not the case with 3D and 4D scans. You can see your baby's skin covering the internal organs. This means that you can actually see the shape of your baby's mouth and nose. You can see her yawn or stick her tongue out. In short, get an idea of whether she looks more like her Mum or her Dad.
The ideal time to have a 3D or 4D scan is between 26 and 32 weeks. This is because, before 26 weeks your baby doesn't have too much fat beneath her skin. So, her facial bones show through the skin. After 32 weeks though, your baby may go deep down in your pelvis. So you might not be able to see her face
Even between 26 and 32 weeks, whether you're able to see your baby's face depends on the position of your baby. If she's lying facing outwards, for example, with a good pool of amniotic fluid around her features, you should be able to see her face very clearly.
However, if she's facing your back, or there's not much amniotic fluid around her, or if you have a large amount of tummy fat, you won't see so much. In this case, your sonographer may ask you to go for a walk and come back for the scan to be repeated. Or she may ask you to come back in a week when your baby may have moved to a better position.
If you're not able to get good views of your baby's face, you may still be able to see her fingers and toes.
From a medical point of view, the benefits of 3D and 4D scans over 2D scans appear to be limited. Also, the special transducers and software required to do 3D and 4D scans are expensive. For these reasons, it's unlikely that these scans will replace normal 2D scans in the near future.
However, 3D and 4D scans can occasionally be useful in giving additional information about a known abnormality. This is because, these scans can show more detail from different angles. So, they can help in the diagnosis of problems such as cleft lip. This can help doctors plan the repair after birth. 3D scanning can also be useful to look at the heart and other internal organs.