First of all, your bridesmaids are your closest friends and relatives and you should be nothing but happy for them. But here are some thoughts on pregnant bridesmaids:
1. Make sure to choose a dress style that is both flattering and comfortable for an expectant bridesmaid. This dress can either be the same dress for all the 'maids or a complimentary style.
2. Think about how far a long she'll be at the wedding. You should have a seat in the front row for her to sit if the service is long or if she gets uncomfortable standing at the altar.
3. Don't make any comments or jokes about her having the baby at the wedding or being too big to walk down the aisle. They are not nice and you may think they're funny, she may not.
4. Allow her to choose her own shoes. Don't insist on heels that she thinks are too high.
5. If you are planning a spa day for you and your bridesmaids check if the spa offers pre-natal massages or other treatments for pregnant women.
6. If she has to pull out from the bridal party for any reason, especially medical, tell her that you're sorry but understand and don't make her feel bad about it. It may be her OB's call and not hers.