This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology and Reproduction, Subject name: Physiology
Which of the following probably triggers the onset of labour? 
Select and explain. 
A. ACTH in fetus, B. ACTH in mother, C. Oxytocin, D. Prostaglandin
A: ACTH in fetus
Answer: A: ACTH in fetus 
Explanation: Ans: a (ACTH in fetus) Ref: Ganong, 22nd ed, p. 451This also is a direct pick from self study MCQs (Chap 23 Q. 17)Mechanism responsible for onset of labour:| Circulatory estrogens due to increase in circulatory DHEAS.So |' gap junction - |' uterine contractions.| GRH by fetal hypothalamus - |' circulatory ACTH - | cortisol leading to maturation of respiratory system.(Thus in a sense fetus picks the time to be bom by | GRH & ACTH secretion)