About 2d scans!

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How comes if my baby at 20 weeks is the size of a banana... how comes on the scans they still like tiny. How would they manage to capture the imagine all in one? If this makes sense!? It's just really bugging me

I wouldn’t say a baby at 20 weeks looks tiny on the scan. At 12 weeks they can fit the whole baby on screen but can’t at 20 weeks.

It's the way the sound waves work. Think of it like vision, you put a book close to your face you can see a limited amount but see more of it as you move it further away.
As baby gets bigger you see less in a single shot on an ultrasound, we have images of whole baby at 12 & 16wk but not at 20wk.