I hid it until 19 weeks, and at 34 weeks was the last time I heard someone sound surprised to find out I was pregnant (not just flabby) I reckon I "popped" around that 33-34 week time.

I'm 170cm, pre-preg weight 69kg. I just had a really little belly that was nursing a 4kg human. Nobody picked it, even my very capable midwife. And especially not my MIL, who blamed my scrawnyness on my vegan diet.