My friend just asked me to be her matron of honor. Yay!

My husband & I are going to start trying for a baby again in June. My friend's wedding is in late October, so in theory I could be up to 5 month pregnant by then.

Unfortunately I have to order my dress to wear at the wedding now, so my question is...should I order 1 size or 2 sizes larger than my normal size? I'm not sure how large a 5 month belly is in respect to fitting in normal clothes. I should also mention that the dress is form-fitting/sheath style.