My fiance and I have had a very long engagement during which one of my bridesmaids became pregnant. Her due date is my wedding date! Even if she doesn't have the child that day, she's probably not going to feel up to walking down the wedding aisle, let alone standing for 45 minutes. Should I ask her to step down?
Rather than asking her to resign her post right away, talk to your bridesmaid and see how she feels about it. You're right that there's a good chance she won't feel up to the occasion on the day of, but she probably still wants to support you -- and frankly, if you asked her to be in your wedding party in the first place, you should want to support her! If she doesn't think she'll be able attend the wedding at all, let her make that decision. Should that be the case, it might be nice to recognize her in the program as an 'honorary bridesmaid,' or something along those lines. If she does still want to attend your wedding, you don't need to ask her to stand up for you -- maybe she can find a nice maternity dress in a similar style or color to your other maids, and of course she can still carry a small bouquet. Simply give her a seat of honor up toward the front rather than asking her to stand and walk with your other bridesmaids.
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Basics for Bridesmaids