My personal opinion is the story about them "saving" Claire's life is a bunch of hooey. Juliet told Ben that the problem developed at the point of conception. The mutation is specific to women who live and conceive on the island. Those that live and conceive off the island are not subject to the same defect. Clair was tested when she arrived on the island to confirm that fact. Then she was implanted in order to be of use to them at a later time. Sun's pregnancy is a little different. We are not really sure if she conceived pre arrival to the island. As was pointed out, her husband may have been healed of his infertility issues when he came to the island. So, if the baby is her secret lover's she should be okay, if it is Jin's she might be doomed.