I'm starting to lean towards another Langoliers time travel theory after tonights episode and the polar bear/dharma discovery in the desert. That makes it appear as if the island is someplace in the past.

In the Langoliers time dies in the past. That could explain why babies can't survive if conceived on the island. They are in the past where life cannot start.

Also, if Locke and Rose are in the past could their bodies have returned to previous healthy state before the flight?

I don't know just a thought.

I don't think its the babies that die, its the mothers.