Congrats!
I was at a wedding where one of the bridesmaids was maybe 7 months pregnant. Another BM was very tall, another was very short, etc. - very disparate body types. They all had their dresses custom made. I think that for the pregnant BM, the seamstress left plenty of extra material, and her final fitting was just a couple of days before the wedding. It looked really good, but couldn't have been cheap!
If the dresses have already been ordered, you could either:
- Take the dress to a seamstress and ask her to alter it
- Take the dress to a seamstress and ask her to create a maternity version of it
- Try to change to a larger size of the same dress and have that altered
- Ask the bride if you could wear a maternity dress in a similar style