Among the 7486 participants included in this analysis, we identified 334 unintended pregnancies. The contraceptive failure rate among participants using pills, patch, or ring was 4.55 per 100 participant-years, as compared with 0.27 among participants using long-acting reversible contraception (hazard ratio after adjustment for age, educational level, and history with respect to unintended pregnancy, 21.8; 95% confidence interval, 13.7 to 34.9). Among participants who used pills, patch, or ring, those who were less than 21 years of age had a risk of unintended pregnancy that was almost twice as high as the risk among older participants. Rates of unintended pregnancy were similarly low among participants using DMPA injection and those using an IUD or implant, regardless of age.