Among many revelations in this episode, I think we learned a lot about how the island 'works' in curing people. I think what it does is super-boost the immune system, so that things uncurable in the rest of the world (paralysis, cancer) are fixed by the body's own immune system. The flip side of that, though, is that the super-boosted immune system overrides the immunosuppression that naturally takes place when a woman gets pregnant to prevent her system from attacking the fetus as a foreign object.

Of course, this still leaves some unanswered questions:

* Why didn't it work to cure Ben? Does it have something to do with how long he's been on the island?
* How is Jacob able to cure Juliette's sister's cancer without bringing her to the island? This could speak to where the real power of the island lies.
* Why didn't this affect Claire's pregnancy? Was it because of how advanced it was (Juliette told Ben that she thinks the problem happens at conception), or did Juliette indeed cure her? Perhaps the implant suppresses the immune system, so it kept Claire alive during her pregnancy, and then they reactivated it to make her sick later.
* How will this affect Jin's pregnancy?