The hormones in birth control pills, the patch, and the ring do three things: they prevent your ovaries from releasing eggs (ovulating), they thicken your cervical fluid, and they thin your uterine lining. Without an egg, there isn’t anything for sperm to fertilize, so pregnancy can’t happen. Additionally, with thicker cervical fluid, sperm have a harder time entering your uterus and swimming to an egg. Finally, should any of the prior mechanisms fail, a thinner uterine lining helps prevent implantation of an egg. It’s a three-pronged approach to effective and safe pregnancy prevention.