Bump measurement?

This may sound stupid but how do midwives measure your bump accurately if you have quite a bit of podge/chub on your stomach 😂 do they go from the start of what your stomach was like and then as it grows follow that.

I didn't even think about this with my first pregnancy as I was quite thin but after having my little lad I found it impossible to get rid of the weight fully, I never thought I'd feel self conscious or worried about it, but now I have extra overhang belly and feel quite embarrassed by my body and weight for this pregnancy 🙈