What are the causes of delayed birth?

We honesty usually don't know.

There's some things that we know can increase the odds that a woman won't go into labor on her own. A badly positioned baby. A first baby. A mother who was a postdates baby herself.

But the understanding of what triggers labor is woefully incomplete. There's a *lot* of people working on it, not so much because of post-term babies (induction is available for them) but for premature babies.