Well, it's not a good idea to expose the fetus to X-Radiation, right? I mean, if your wife consents to it, and the physician will permit it, you in theory could do it -- but that's a risk I really don't think you should be taking -- at all.
If you do EE and have her listed as not-accompanying, that will mean another application later (for your spouse and your child) that will take time and money for sponsorship.
I am not an expert on EE (or immi for that matter). I have completed my wife's process, and I like to think I am the backbone for the inland 2016's. But in my opinion, I would suggest just starting your application, and keep your wife listed as accompanying.