Does the effectiveness of the nuvaring decreases if i use it for 4 weeks?

No- total of 4 weeks: If the NuvaRing is left in for a total of 4 weeks or less the risk of pregnancy is still low. Remove the ring/ insert a new ring after a 7 days ring-free period. If the ring had been left in for > 4 weeks the risk of pregnancy increases, do a pregnancy test to make sure you are not pregnant.Use a back up birth control like condoms till the new ring has been in place for 7 days in a row. Take care.