OMG how would they know that? It would have to be an assumption based on where the little embryo had implanted, I would think. Or maybe they could see the empty cyst on the ovary that the egg had popped out of?

I wouldn't imagine it would mean anything in particular for your child though. The gender of bubs is determined based on whether it gets and X or a Y from dad. Although, metaphysically, the left side represents Ying, Female, Receptive, etc. But that's not enough to affect gender!