The intrauterine device, or IUD, is the most effective form of reversible birth control available to women. New research shows that when the small, T-shaped device is inserted into a woman’s uterus to deter sperm from reaching an egg, it’s 20 times better at preventing pregnancy than the birth control pill, the hormonal patch, or the vaginal ring. Condom failure rates are even worse. In one study, 75 percent of women said they’d prefer an IUD to alternate forms of contraception. Still, only 5 percent of women actually use them.