Which of the following hormones is not involved in parturition? 

Progesterone does not promote parturition but rather helps maintain pregnancy.

The signals for parturition originate from the fully developed foetus and the placenta. This triggers release of oxytocin from the maternal pituitary. Oxytocin acts on the uterine muscle and causes stronger uterine contractions, which lead to parturition. 

Cortisol increases prostaglandin production by the placental and fetal membranes, thereby promoting cervical ripening and uterine contractions. 

Estrogen upregulates the receptors for oxytocin on the myometrium and increases the number of gap junctions in the myometrium.