You put your finger up there and see if you feel the 'strings' that hang down but of course if you have never checked it before you won't know if it is still in the original place. 30 years ago I had an IUD which I checked the strings all the time and one day in the shower it fell out....then it dawned on me I had missed a period...resulting in baby #4. Nothing is 100% I guess. Good luck.