To investigate the effects of the Affordable Care Act (ACA) and its elimination of cost-sharing on contraception utilization, pregnancy rates, and abortion rates. We conducted a retrospective cohort study within a healthcare system serving over 4.5 million insured members across 21 medical centers and 250 clinics. The study included women aged 18-45 with continuous health plan membership for at least two years in the pre-ACA (2007-2012) and post-ACA (2013-2018) periods. We analyzed out-of-pocket (OOP) costs for contraception, including oral contraceptives and long-acting reversible contraception (LARC), before and after the ACA's implementation. We then examined how the elimination of OOP costs affected contraception use, pregnancy rates, and abortion rates. The study identified 1,523,962 women of childbearing age. In 2013, cost sharing for contraception sharply declined, with average annual OOP costs dropping from $88-$94 pre-ACA to nearly zero post-ACA. Contraceptive use increased overall, rising from 30.2% pre-ACA to 31.9% by the study's end, with a notable rise in LARC use. In interrupted time-series analyses, while contraception use continued to increase post-ACA, new pregnancy rates declined at a faster rate than pre-ACA, and abortion rates continued to fall, though at a slightly slower pace than pre-ACA (p<0.05 for all trends). The Affordable Care Act's elimination of contraception cost-sharing led to increased contraception use, particularly LARC methods, and contributed to declines in both pregnancy and abortion rates. This suggests that improving access to effective contraception is a key strategy in reducing unintended pregnancies.