What makes some babies come early, and some come late? What tells the female body that it’s time to start labour?

Question

What makes some babies come early, and some come late? What tells the female body that it’s time to start labour?

In: Biology

Answer 1

Delivery of the baby should happen when the fetus is matured enough but before the placenta has reach its end-of-life. The breakdown of the placenta triggers the labour process, according to this article https://www.sciencedaily.com/releases/2015/10/151026132136.htm

Now why does it make sense, evolutionary wise?

The mothers (human, animals) which did not have the right aging of the placenta did not induce labour and died during childbirth (too long lived placenta) or delivered non-matured fetuses (too short lived placenta). As such the genetic blueprint for the right-aging placenta survived.

Now the question of why some are coming too early and too late? Because 40 weeks is not the only time they can survive or be delivered, 39 weeks is fine, 38 weeks is fine, 41 weeks is fine.