Thanks for your query.
It is not necessary to get pregnant everytime with unprotected sex.
So even in the coil fell out, getting pregnant is not the norm.
Secondly the coil might just have moved upwards in the uterine cavity
, and that is why the string might not be visible or palpable.
If you are not having irregular periods
or symptoms, chances of pregnancy
are very low.
Only a scan will tell you if the coil is actually in position.