Ans. is 'c' i.e., Inhibition of motility of the uterine tubes Mechanism of action of OCPs 1. Inihibition of gonadotropin release from pitutary by reinforcement of normal feedback inhibition No prevulatory LH surge No ovulation This is the most impoant mechanism. Thickning 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.