As a seamstress, I often have to do some drastic alterations. Not because young ladies are changing 2 - 3 sizes, but it is recommended by dress shops to order large. This practice is to generate more business for their alterations department.
I hope most mothers & daughters don't buy into this thinking. I understand a single size up, never more than that please! People are spending more on alterations than on the dresses they purchase.
It's easy to comply to the sales staff, who wants to order wrong at a time like this? Make sure you roll altering costs into your budget and know costs for each item altered before you agree to the work.
Don't get me wrong, I make money doing this. It is labor intense and compensation should be fair. However, buying a dress, multiple sizes too big, just for the sake of altering is wrong. If something seems fishy when going through the process, then it is most likely fishy. Trust you natural instincts!
Buying too small in hopes of weight loss is not a good idea either! I have had to enlarge gowns in the past & it is humiliating for the wearer to submit to the process. The likelihood of this happening is slim. So, next time you have input at a fitting for someone you love, follow your common sense. If alterations need to be made, be prepared for the cost.
So, one last thing...once you have had a fitting, don't let your weight fluctuate one way or the other. I've had this happen, the cost, financially and emotionally is tough. Be where you want to be "size-wise" when you order your dress and through your original fitting.
All this stress will be forgotten and replaced with with the story of your wedding. As it should be!