Can the yolk sac move?

Hi,

Does anyone know if the yolk sac can move? I went for a private 10 week scan on Friday and I needed a wee so much she let me go half way through. I've just been watching the videos and it looks like the yolk sac has moved from one side to the other side before and after I emptied my bladder. Does anyone have any experience of this? Twins run in my family (I'm a twin myself) and I just wonder if it could be a hidden twin.

I've attached photos from before and after.

I can't get a screenshot with baby in but the yolk sac is near the feet - this is before.

After the yolk sac is near the head.