This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Contraception, Subject name: Gynaecology & Obstetrics
All are mechanisms of IUCDs except: 
Select and explain. 
A. Chronic endometrial inflammation, B. Increase the motility of tubes, C. Inducing endometrial atrophy, D. Inhibition of ovulation in >80% of the users
D: Inhibition of ovulation in >80% of the users
Answer: D: Inhibition of ovulation in >80% of the users 
Explanation: Mechanism of Action: Several mechanisms are responsible for the contraceptive effect of an IUCD. The presence of a foreign body in the uterine cavity renders the migration of spermatozoa difficult. A foreign body within the uterus provokes uterine contractility through prostaglandin release and increases the tubal peristalsis so that the feilized egg is propelled down the fallopian tube and more rapidly than in normal and it reached the uterine cavity before the development of chorionic villi and thus is unable to implant. The device in situ causes leucocytic infiltration in the endometrium. The macrophage engulf the feilized egg if it enters the endometrial tissue which inimical to the implantation of the feilized ovum Progesterone-carrying device causes alteration in the cervical mucus which prevents penetration of sperm, in addition to its local action. It also causes endometrial atrophy. It prevents ovulation in about 40% Ref: Shaw&;s textbook of Gynaecology 17th edition Pgno: 261