Delivery means actual birth of the foetus.
During pregnancy, most of the oestrogens are present in a binding form. During the last trimester, more free oestrogen appears increasing the excitability of the myometrium and prostaglandins synthesis. Although oxytocin is a powerful stimulator of uterine contraction , its natural role in onset of labour is doubtful. The secretion of oxytocinase enzyme from the placenta is decreased near term due to placental ischaemia leading to predominance of oxytocin's action. This explains the preterm labour in case of multiple pregnancy and polyhydramnios.