It's as safe as if you were not pregnant. If you're prone to altitude sickness you should know that they will have oxygen masks for people who get lightheaded.
Ugh! Im so jealous. Some of my family was just there and I'm wishing I could go.
youll probably have the same issues as with altitude sickness since the air is very thin. You may get whoosy. What kind of altitude are you at now? And always stay very hydrated because the thin air dries you out. But other than that- id totally go for it.