The society of an island nation is led by a religion known as "The Church of the Eternal Mother", it is an ancient faith that adheres to a fertility goddess. This faith is led by five elderly women called Mannas Natau, at least one of whom will regularly become spontaneously pregnant. These elders are biologically immortal and are worshipped as avatars of the Eternal Mother: mortal vessels of the goddess's power responsible for creating life and growing the numbers of the community. Children born from the goddess are immune to all illnesses and live longer than other humans, but are not immortal. The goal of the community is to ultimately build an empire by conquering its neighbors.
The elders have inherited a mutation in their biology which allows them their long lives. Cells during a normal life cycle multiply at a rapid rate, constantly dying and being replaced by new cells. This ability to proliferate doesn't happen indefinitely, decreasing as the individual gets older. Cells begin to produce errors in copying themselves, contributing to the person aging and eventually dying. The reason for the longevity of the elders is due to an immortal cell line, which evades normal cellular senescence and continually undergoes cell division. This ultimately gives the elders their immortality, allowing them to rapidly regenerate from wounds and protects them from natural illnesses. However, their is a natural downside to this. As they age, it becomes harder to produce live children. The amount of stillbirths increase as they get older, to the point where 90% of children are born dead.
What role could their natural longevity play in the creation of this problem?