I would say yes to the bike riding. The skating I would say check with your doctor. The skiing I definitly would say no to. The sledding as well. I would stick to making a nice snowman this Christmas lol.
I'm going to have to agree with mama.
Bike riding should be fine, but winter sports are probably going to be a no-no just for the sheer fact that you could fall and hurt baby. I'm always skating, skiing and snowboarding in the winter and I still fall down all the time. And it's usually a face plant...landing on the belly while pregnant wouldn't be good.