Remember what they did on Deep Space Nine when Nana Visitor got pregnant, but it didn't fit her character? They contrived a situation where she had to surrogate-carry a baby for Keiko O'Brien.

So:

#1 Rand knocks up Aviendha early in AMOL. This is already probable, because readers will need to have doubts about Rand's survival.
- #1a Also, there's the problem of Lanfear's superpowered lust inducement that has the potential to bring Rand down. No doubt there will be situations where Rand's proper ladies will have to be on hand to *cough* quench his fires.

#2 Elayne is mortally wounded. The babies! The babies!

#3 Nynaeve arrives on the scene and asks, quite casually, if anyone happens to have a functioning womb that's already delivering nutrients?
- #3a Reread the prologue of Winter's Heart, where Aviendha and Elayne become first-sisters. It goes beyond simple ceremony; it requires channeling, includes a weird sort of rebirth, weaves related to the Warder bond, and the conspicuous absence of Melaine owing to concern that her unborn babies might be touched by the weave. There's just tons of foreshadowing there.

#4 Viola! The babies are transplanted. Elayne dies. Aviendha carries and gives birth to four babies, and the "something odd" is the obvious fact that two of them are Elayne's.