I was just talking to a classmate about this.
From Andrew Sullivan:
A study in this week’s New England Journal of Medicine points to the IUD:
The results were striking: women using pills, patches, or rings “had a risk of contraceptive failure that was 20 times as high as the risk” among those using IUDs.” And, much as the authors had hypothesized, women younger than 21 who chose to use a pill, patch, or ring—rather than an IUD—were twice as likely to become accidentally pregnant than older women. … The study’s conclusion runs a single, unequivocal sentence: the effectiveness of IUDs is simply superior to other contraceptives. “If there were a drug for cancer, heart disease, or diabetes that was 20 times more effective,” said [senior author Jeffrey Peipert], “we would recommend it first.”
Most of the rest of the world has caught on, compared to the 1 in 20 American women who use it:
A 2011 study from the World Health Organization reports that, in China, a full third of married Chinese women use so-called “long acting” devices. In Scandinavia, nearly 20 percent do. The highest users? Vietnamese and Egyptian women, at around 35 percent. Only in sub-Saharan Africa are IUDs less popular than in the Americas.