Which of the following hormones is not involved in parturition?

The correct answer is Option (3) → Relaxin

Parturition is the process of childbirth. It is started by a complex neuroendocrine mechanism. The signals come from the fully developed foetus and the placenta. They cause mild contractions of the uterus, called the foetal ejection reflex. This makes the mother’s pituitary release oxytocin, which causes stronger contractions and pushes the baby out. The hormones named for this mechanism are cortisol, estrogens and oxytocin.

(1) Cortisol — Involved in parturition. Cortisol is one of the hormones of the neuroendocrine mechanism that starts parturition.

(2) Oxytocin — Involved in parturition. Oxytocin acts on the uterine muscle and causes the strong contractions that expel the baby.

(3) Relaxin — Not involved in parturition. Relaxin is a hormone secreted by the ovary in the later phase of pregnancy. It is not one of the hormones named for inducing parturition.

(4) Estrogen — Involved in parturition. Estrogens also take part in the mechanism that starts childbirth.

NCERT Extract:
Parturition and Lactation – “… Parturition is induced by a complex neuroendocrine 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.”
Pregnancy and Embryonic Development – “… In the later phase of pregnancy, a hormone called relaxin is also secreted by the ovary.”