Give scientific reasons: When the time of birth is near,two chemical signals are associated to produce real parturition pain (labour pain).

(A) The signals for parturition originate from the fully developed foetus and the placenta,which induce mild uterine contractions called the foetal ejection reflex.
This reflex triggers the release of $Oxytocin$ from the maternal posterior pituitary gland.
$Oxytocin$ acts on the uterine muscle and causes stronger uterine contractions,which in turn stimulates further secretion of $Oxytocin$.
Simultaneously,the placenta releases $Prostaglandins$,which further enhance uterine contractions.
The stimulatory reflex between the uterine contraction and $Oxytocin$ secretion continues,resulting in stronger and more frequent contractions,leading to the expulsion of the baby out of the uterus through the birth canal.