How can I discourage this?
When he sees us heading up/down the stairs, he races up quickly, often getting under our feet and tripping us.
When he doesn't to that, he lays at the top of the stairs so we try to climb over him and plays with our feet. If he senses we're cautious, he then rushes down a couple of steps and stops to plays with our feet whilst refusing to move unless you climb a whole step over him.
Each of us have had falls down the stairs before DCat (who we've now had for 4 months and he's nearly 8 months) and I don't want him to keep tripping us up, especially as I'm pregnant.