Ans. A. By Causing early ovulation.Methods of emergency contraceptionThere are two methods of emergency contraception:# emergency contraception pills (ECPs)# copper-bearing intrauterine devices (IUDs).When inserted within five days of unprotected intercourse, a copper-bearing IUD is the most effective form of emergency contraception available.The emergency contraceptive pill regimen recommended by WHO is one dose of levonorgestrel 1.5 mg, taken within five days (120 hours) of unprotected intercourse.1. Emergency contraception pills# WHO recommends levonorgestrel for emergency contraceptive pill use. Ideally, this progestogen-only method should be taken as a single dose (1.5 mg) within five days (120 hours) of unprotected intercourse. Alternatively, a woman can take the levonorgestrel in two doses (0.75 mg each; 12 hours apart).# Mode of action :Levonorgestrel emergency pills prevent pregnancy by preventing or delaying ovulation. They may also prevent fertilization of an egg by affecting the cervical mucus or the ability of sperm to bind to the egg. They are not effective once the process of implantation has begun.# Effectiveness :levonorgestrel regimen is 52-94% effective in preventing pregnancy. The regimen is more effective the sooner after intercourse it is taken.2. Copper-bearing intrauterine devices (IUDs)# WHO recommends that a copper-bearing IUD, as an emergency contraceptive, be inserted within five days of unprotected intercourse. This may be an ideal emergency contraceptive for a woman who is hoping for an ongoing, highly effective contraceptive method.# Mode of action : As emergency contraception, the copper-bearing IUD primarily prevents fertilization by causing a chemical change that damages sperm and egg before they can meet.# Effectiveness: When inserted within five days of unprotected intercourse, a copper-bearing IUD is over 99% effective in preventing pregnancy. This is the most effective form of emergency contraception available. Once inserted, she can continue to use the IUD as an ongoing method of contraception.# Postcoital contraceptivesDrugsDosePregnancy rate (%)Levonorgestrel0.75 mg stat and after 12 hours0-1Ethinyl estradiol 50 mg + Norgestrel 0.25 mg2 tab stat and 2 after 12 hrs0-2Conjugated estrogen15 mg BD x 5 days0-0.6Ethinyl estradiol2.5 mg BD x 5 days0-0.6Mifepristone10 mg single dose0-0.6Copper IUDsInsertion within 5 days0-0.1