If you go late you could still be in hospital (particularly if you have a c section). That in itself could not only cause issues with letting the bride and groom down, but also your partner doing the same thing as he'll want to be with you and bubs. I'd be bowing out gracefully and just attending as a guest if you can manage it.

If you had already had bubs there will be no way of predicting what size you will be at that time so your dress is going to cause dramas for the bride & you will also be likely to stress about that too, shoes could be an issue too if you get swelling and your feet haven't yet recovered (some women stay a bigger size after pregnancy). You will not need the added pressure during your first precious weeks with a new bub.

Attending a wedding as a guest is far more fun than as a member of the bridal party anyway so it's not like you are missing out on anything really.