system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When a woman goes into labour, is it her body that decides the baby is ready, or does the foetus send some sort of signal to the mother's body to say it's ready to come out?

As above.  Also, how would the answer to this title question explain babies that are born premature, or babies that are born so late that the labour has to be induced?

Thank you in advance!  I have wondered this for a while!
gpt
pregnancy is a continuous process. mother, baby, and placenta are constantly exchanging messages in the form of hormones, nutrients, and immune cells. 
its is thought that once a fetus’s lungs are developed, a signal is sent from the fetus to the mother that first initiates labor. that signal causes a “cascade” to begin. mom’s body releases estrogen, baby changes position and starts pressing on the cervix, the cervix starts changing, etc.