NuvaRing® is as effective as the Pill when used as directed, but you don’t have to take it every day. You leave
NuvaRing® in place for 3 weeks, then remove it for a 1-week ring-free
period. You should get your period during this “week off.” (Using NuvaRing® as prescribed, you will continue to be protected from pregnancy during the ring-free week.) Exactly 1 week after you take NuvaRing® out, you insert a new one."
From : http://www.nuvaring.com/Consumer/aboutNuvaRing/index_flash.