Once uterine contractions have begun the female body releases several hormones that act in a positive feedback loop. the purpose of this feedback loop is

The purpose of this feedback would be to deliver the baby.

Uterine contraction will cause the release of oxytocin that in turn will increase the uterine contraction too. This mechanism is called positive feedback because the effect will keep increasing as the time pass. This mechanism will be over when the objective is completed, in this case when the baby delivered. 

Ithink its c hope it : )