The simple answer to this question is yes, but there are some limitations. No matter what, you should always console with your doctor to ensure that they do not recommend otherwise. If they give you the all-clear, then you are set to go. With this being said, backpacking can cause physical stress. In addition, as Dr. Rob Shire of Manhattan has explained, areas causing nervous stress on the spine can interfere with the development of the fetus. Because the nervous system controls all the life in the body, this can compromise the pregnancy. Plus, having the extra weight on your back can impact your delivery.
This is a situation where you should adhere to your doctor’s advice. They are the experts and they will be able to clarify to you if you can handle it.