Contraceptive failure in the United States: an update.

This report provides an update of the authors' previous estimates of first-year probabilities of contraceptive failure for all methods of contraception. Estimates are provided of failure during typical use (which includes both incorrect and inconsistent use) and during perfect use (correct use at every act of intercourse). The difference between these two probabilities provides a measure of how forgiving of imperfect use each method is. These revisions are prompted by recent studies that provide the first estimates of failure during perfect use for periodic abstinence and the cervical cap, by more complete evaluations of implants, and by the appearance of the Copper T 380A and disappearance of other IUDs from the US market. Also provided is a more complete explanation of how the previous estimate of the probability of becoming pregnant while relying solely on chance should be interpreted, and this estimate is revised slightly downward.