They reduce pregnancy because the delay the uterus releasing the egg, and delay ovulation. Less than 1% of women who use IUDs pregnant, although pregnancies after the emergency contraceptive pill are not as rare.
Answer: Research shows that emergency contraception pills work mostly by preventing or delaying ovulation (the release of an egg from the ovary). Less commonly, emergency contraception may prevent fertilization of the egg by the sperm if ovulation has already happened.
