is the hormone that is released by the mother's pituitary gland that is responsible for initiating contractions in the uterus as a precursor to labor.

Oxytosin

Explanation:

Oxytosin is an important hormone secreted by the pituitary gland and has a variety of functions including but not limited to:

Sexual reproduction Initiation of labour in pregnant women by stimulating the contraction of the uterine muscles and increased prostaglandin production Onset of lactation and breastfeeding