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About half of the unintended pregnancies in the United States result from contraceptive failure, rather than from nonuse of contraception. Some contraceptive methods may be more prone to failure than others, due to possibility of inconsistent or incorrect use, but little data have been available to directly compare the efficacy of different methods.
The Contraceptive CHOICE Project evaluated the rates of unintended pregnancies associated with different forms of reversible contraception in 7,486 women aged 14-45 years desiring to postpone pregnancy for at least 1 year. Women were given their choice of contraceptive at no cost and followed for up to 3 years. Choices included intrauterine device (IUDs), subdermal implant, oral contraceptive pill, transdermal patch, vaginal ring, and depot medroxyprogesterone acetate (DMPA) injection. Prior to selection, all women were read a standardized script describing the efficacy of IUDs and implants and were counseled about the risks and benefits of all reversible contraceptive methods. IUD or implant was chosen by 77.2%, pill, patch, or ring by 20.4%, and DMPA injection by 2.4%.
There were 334 unintended pregnancies during follow-up. The contraceptive failure rates per 100 person-years were 0.27 with IUD or implant, 0.22 for DMPA injections (not significant vs. IUD or implant), and 4.55 for pill, patch and ring combined (p< 0.001 vs. IUD or implant and vs. DMPA injection) (level 2 [mid-level] evidence). Cumulative failure rates over 3 years were 0.95% with IUD or implant, 0.7% for DMPA injections (not significant vs. IUD or implant), and 9.4% with pill, patch or ring (p < 0.001 vs. IUD or implant and vs. DMPA injection). In a subgroup analysis of pill, patch and ring users, women < 21 years old had a significantly higher risk of unintended pregnancy than older women (adjusted hazard ratio 1.9, 95% CI 1.2-2.8). There were no significant differences in pregnancy rates associated with age in women using IUD or implant or in women using DMPA injections (N Engl J Med 2012 May 24;366(21):1998).
For more information, see the Contraception overview topic in DynaMed