The secretion of which of the following hormones is controlled by positive feedback mechanism?

The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex. This triggers release of oxytocin from the maternal pituitary. Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which in turn stimulates further secretion of oxytocin. This is positive feedback loop.

Testosterone, PTH and thyroxine exhibit negative feedback.