This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
[{'content': 'Mechanism of action of oral contraceptive pill can be all except ? \nSelect and explain. \nA. Hostile to sperm penetration, B. Anovulatory cycle, C. Failure of blastocyst implantation, D. Blockade of fimbrial ostia', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., Blockade of fimbrial ostia Mechanism of action of OCPs 1nihibition of gonadotropin release from pitutary by reinforcement of normal feedback inhibition - No prevulatory LH surge - No ovulation This is the most impoant mechanism. Thickening of cervical mucus secretion (due to progesterone) - hostile to sperm penetration. Even if ovulation and feilization occur, the blastocyte fails to implant because endometrium is either hyperproliferative or hypersecretory - not suitable for nidation - Impoant in case of postcoital pill. Uterine and tubal contractions may be modified to disour feilization. Postcoital pills may dislodge a just implated blastocyte or may interfere feilization/implantation.", 'role': 'assistant'}]