I would up until maybe 5 to 5 1/2 months. After that bump just gets in the way.
I body surfed last time I was pregnant (4 months I think). But I kept rolling off the board!
I went backapacking in Iceland 2 weeks ago at 6 months pregnant. Admittedly this didnt involve skiing, but it did involve pulling a suitcase and tent around, camping in a storm in a leaky tent and doing about a 1/2hour climb up a steep hill pulling all my luggage.
If youve been healthy so far I think being pregnant isnt as delicate state as its made out to be. After all women work physically hard in 3rd world countries nearly right up until the birth. And then afterwards there right back out in the fields with babies strapped to their backs. Im not advocating it as a good idea, but I think the human body is more reslilent that we think. I guess only you know how healthy you are. I seem to have textbook pregnancies so im not too worried about losing my babies. I can see for some women pregnancy is a most delicate time.
Good luck whatever you do.