Maggie Sottero Sizing Question

I know most wedding gowns run a size or 2 smaller than "street clothes". My question is for anyone who has ever worn a Maggoe Sottero fitted bridalk gown ( not a ball gown since the flared skirt can accomodate most hip sizes). Anyone whose worn a Maggie S ( particularly a mermaid or sheath cut gown, did you find you had to purchase 1 or 2 sizes larger than you normally wear? Say you wear a size 8 normally, did you have to get a gown in size 10 or 12? I`m hoping to secure the Misha gown in size 12 and normally wear a size 12 in "street clothes". I just want to know if its realistic to think that if I continue on my exercise routine I`ll be able to wear this gown come the fall. ( Better stop eating thie TXIX!!) Please let me know.