system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does the uterus know when exactly to start contractions to birth a human baby?

Thought this when I wondered how premature births happen and why the body does that.
gpt
The baby puts pressure on the cervix. Through a biochemical pathway your brain releases oxytocin. Oxytocin causes the walls of the uterus to contract. The contraction pushes the baby against the dilating cervix, and the pathway repeats.