<prompt> Which of the following is true regarding RU 486?Prevents feilizationHas affinity for estrogen receptorsSingle dose of 10mg prevents pregnancy in 90 casesCauses delayed menstruation  <response>: RU 486 mifepristone does not prevent feilization. It has affinity for progesterone receptors. It blocks the action of progesterone on the endometrium. It prevents implantation by causing sloughing and shedding of decidua. Single dose of 10mg prevents pregnancy in 99.1 cases. Ref: Shaws Textbook of Gynaecology, 18th edition, p237 