The NuvaRing is a method of birth control that works by releasing the hormones progestin and estrogen directly into the vagina. This method is an alternative to other methods made especially for those who do not prefer pills, skin patches, intrauterine devices, injections or implantable devices.
When the ring is inserted into the vagina, the body recognizes that estrogen and progesterone are coming from somewhere else (the ring), so the ovaries do not need to release those hormones. While using the ring, your hormones temporarily go to sleep. While they are "napping," they do not release hormones, and do not cause the release of an egg, which is how the ring works to prevent pregnancy.
Forgetting to use the ring as directed can cause the ovaries to "wake up." When that happens, the ovaries release hormones and may release an egg, which can result in pregnancy.