"The main source of contraceptive failure comes from those methods that require adhering to some schedule, such as birth control pills or condoms," says James Trussell, PhD, director of the office of population research at Princeton University and the author of review on contraceptive failure published in the journal Contraception in August. "The main reason they fail is not that they are used and fail, but because of imperfect use."
"Methods like condoms, cervical caps, diaphragms and spermicides, must be used every single time you have sex," he continues. And things happen, condoms break and microscopic holes form in diaphragms, compromising the barrier between sperm and the vagina. But the most common mistake people make is not using any method at all. "The way these are most often misused is that they are in the bathroom cabinet or in the drawer next to the bed rather than in the vagina or on the penis," he says. Likewise, women taking oral contraceptives may forget to take their pill.
How well a contraceptive methods works must be weighed in terms of perfect and typical use. This is the difference between following the method's directions by the book and using it inconsistently and incorrectly. According to Dr. Trussell's review, when using the male condom for example, 16 percent of women experienced an unintended pregnancy over the course of one year with typical use and 6 percent got pregnant with perfect use.
