pregnancy 1, it was around 18 weeks. I looked slightly bigger around the belly from 14-16 weeks or so, but by 18, there was an evident bump. But not so much that you'd know for sure - we kept it a secret until 22 weeks.

pregnancy 2, I reckon it was obvious from around 14-16 weeks there was a bump, but as I'm a bit tubby, it wasn't obvious whether it was too many pancakes, or a bun