I had the same question when I went to Vail, CO (11,000+) in January (I live in Wisconsin so pretty much no elevation.) My doctor said it wasn't a problem. He said the babies will take the oxygen they need and may leave you a little short of breath. I think he said they have a lot of hemoglobin (or maybe that it is just really good, something about their hemoglobin

). Just stay hydrated. I was really thirsty but I didn't have any problems.