Many people claim that the pregnancy problems began sometime after 1977, but is there any evidence to support this?
Juliet's medical opinion of the defects stipulates that the problem occurs at conception, i.e. if you conceive a child on the Island, chances are that you and your baby will die just before you enter the third trimester. This is supported by the births of Jacob, the Man in Black, Alex and Aaron. However, it would appear that if, like Sun, you conceive on the Island, but leave, then the baby will be perfectly healthy, exemplified by Ji Yeon's birth. It appears, therefore, that as long as the mother is not on the Island at this critical stage of entering the third trimester, then she and the baby should be fine.
The birth of Ethan Goodspeed in 1974 led many people to believe that the pregnancy defects did not exist on the Island at this point in time, but what evidence is there that Amy Goodspeed spent the end of her second trimester on the Island? It is perfectly conceivable to think that the DHARMA Initiative knew full well of the complications, and used the Staff station in order to identify the defect and ultimately combat it. So couldn't Amy have been shipped off to Ann Arbor for the majority of her pregnancy? Consider that this is a feasible possibility. So the question remains, if the pregnancy problems always existed, what is the cause?
The Source. The light is life, death, rebirth. I believe that the Source is the reason behind the Island's healing powers. Rose and Locke were cured of their ailments because of their proximity to this mysterious light. The light is glorious and deadly in equal measure. So can we assume then that this healing power boosted the immune system of the mother so much that the fetus is rejected? I know this has already been stated, but now that the Source can be viewed as the Island's healing power, and we know that the Source has existed for years and years (maybe since the beginning of time), then we can propose a theory that maybe the pregnancy defects have been a constant feature of the Island just as the power of the Source has been. Thoughts?