I just sat down on a dining chair legs sort of crossed for 4 hours while using laptop. i did get up a couple of times to eat etc. dvt? i'm pregnant.

Unlikely: That's unlikely to cause a DVT. In terms of diagnosis, the hallmark of a DVT is unilateral swelling. If one leg has newly become significantly more swollen than the other, see your doctor.

Whoa!: If just sitting still caused DVTs, everyone would be dead soon, pregnant or not. That said, is it "absolutely impossible" to get a DVT as you described? No--just extremely unlikely. DVTs are UNCOMFORTABLE--that is what prompts Dr visit. Do you have a new pain in your leg? Is it hot compared to other one? Swollen (or more so) compared to other one? If no to these, then I would not worry.