It produces a 2-dimensional (2-D) black and white image that gives only a side view of the baby.
In some areas, it may be carried out later than 21 weeks.
The anomaly scan is offered to everybody, but you don't have to have it if you don't want to.
The mid-pregnancy anomaly scan looks for some physical abnormalities in the baby.
The scan only looks for these problems, and can't find everything that might be wrong.
The scan checks for major physical abnormalities in your baby, although it can't pick up every problem.
The anomaly scan is carried out in the same way as the dating scan.
This, together with the increased blood supply to your skin, can lead to varicose veins.
If you’re one of the unlucky ones getting rudely awoken by sudden sharp pains in your leg, try gently exercising your legs, ankles and feet during the day - and see if that prevents it.
After 16 weeks, lying - or exercising - on your back can sometimes cause low blood pressure and dizziness.
Try to avoid lying on your back for long periods of time.
Alternatively you can call the Tommy's Pregnancy Line on 0800 0147 800; or email us at .