contraceptive effectiveness, the effectiveness of a method of contraception in preventing pregnancy. For clinical purposes it combines the theoretic effectiveness of the device, medication, or method and the use effectiveness. It is sometimes represented as a percentage but more accurately as the number of pregnancies per 100 woman-years. The average pregnancy rate for a couple who are sexually active and do not use contraceptives is equivalent to 85 pregnancies per 100 woman-years. A contraceptive method that results in a pregnancy rate of fewer than 10 pregnancies per 100 woman-years is considered highly effective. See also pregnancy rate, woman-year.
