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': 'Newer progestational contraceptives primarily act by: \nSelect and explain. \nA. Oviductal motility, B. Uterine endometrium, C. Cervix, D. Inhibiting ovulation', 'role': 'user'}, {'content': 'Answer: D \nExplanation: FOGSI is Federation of Obstetrics and Gynaecological Societies of India and the highest governing body in Obs and Gynae in India.\nProgesterone only pills act mainly by causing thickening of cervical mucus.\nProgesterone only pills\nMechanism of action of POP\'s is mainly on cervical mucus -\n\n"All Estrogen free pills except the newer desogesterel pill primarily rely on changes in cervical mucus as they do not inhibit ovulation consistently."\nThe cervical mucus effect peaks within 3-4.hours after taking the tablet and lasts for about 22 hours. Hence the next tablet must be taken within 27 hours of the preceeding tablet or else the contraceptive benefit of the cervical mucus effect will decrease and finally subside.\nUnlike COC\'s that almost always prevent ovulation, traditional POP\'s (progesterone only pills) inhibit ovulation in 40-50% of cycles. "A randomized double blind study, performed over 13 cycles showed that 75 lig desogestrel daily was sufficient to inhibit ovulation in 97% of cycles. Hence for newer POP\'s containing desogestrel the primary mode of action is inhibition of ovulation". - FOGSI Focus Jan 06 issue on Modern pill, Chapter Estrogen free pill p 41\nThus, for newer progestational agents main mechanism of action is by inhibition of ovulation.\n\nRemember\n\nTraditional POP\'s are also known as Low-dose progestogen only pills.\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\xa0\nMain progesterone used are:\xa0\xa0\n\xa0Norethisterone 350 mcg\nNorgestrel 75 mcg\nLevonorgesterel 30 mcg\nTheir main mechanism of action (as discussed earlier) is thickening of cervical mucus.Q\n\tThey also:\nRender endometrium unsuitable for implantation\nAccelerate tubal motility\nDisturb corpus luteal function.', 'role': 'assistant'}]