This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Non communicable diseases, Subject name: Social & Preventive Medicine
Least chances of pregnancy is with - 
Select and explain. 
A. OCP, B. IUCD, C. Coitus interruptus, D. Condom
A: OCP
Answer: A: OCP 
Explanation: park's textbook of preventive and social medicine 23rd edition. *Oral contraceptive of combined type are almost 100 effective in preventing pregnancy.some women do not take it regularly so the actual rate is lower.mechanis of action:prevent the release of ovum from ovary.this is achieved by blocking pituitary secretion of gonadotrophin.progestogen only preparation render the cervical mucous thick and scanty and there by inhibit sperm penetration.