Ethan is born on the Island and is in fact the child of two members of the Dharma Initiative in, I believe, 1974.
In 1977, the Swan is yet to be built or at least finished. Some time later, the Swan is completed, the Incident happens, and the procedure of pressing the button is put in place. A failsafe key is installed that could 'wipe it all away', however, pressing the button every 108 minutes has the benefit of keeping the Island in place and in sync with the outside world.
Hidden away, the Swan goes unnoticed by the Others, although, one of it's effects may very well have been felt by them and Dharma as well.
Sometime between the birth of Ethan, in 1974, and our introduction to the Island, in 2004, a mysterious and unsolvable issue began occuring with all mothers who conceived on the Island. Could it be, by not using the failsafe key and pressing the button instead, that the Island's natural functions are disrupted in some way and that some how this is causing the birthing issue?