What are the chances of an egg being fertilized on the implanon but terminated because it wasn't able to attach itself to the lining of the uterus? i've been using the implanon for 2 years but i'm afraid that i might be killing fertilized eggs?

It is possible. One of the known effects of Implanon is to make harder for a fertilized egg to attach to the uterus, but I am not sure what the chance is. The primary effect of Implanon is still to prevent ovulation.

As my colleague notes, the main way implanon works is to prevent ovulation. It also changes cervical mucous to make it harder for sperm to reach the egg. However, no birth control method is 100% effective (except abstinence!). So fertilized eggs may not implant as Implanon also changes the lining of the uterus. Pregnancy is still possible but it is more common to be ectopic with Implanon

I can't give you an exact percentage, as I don't know if very good studies have been done to answer this question. It sounds like the idea of a fertilized egg, not implanting, troubles you. I won't to get into the issue of "killing a fertilized egg", I realize this can raise ethical questions and I respect yours. Please realize that nature itself often results in fertilized eggs miscarrying.