No. It won't raise your premium. Your plan is a group plan and underwritten as such--that is, you are most likely paying based on your group's experience (and it might even be self-funded, generally depending on the size of your employer). Rules for group health insurance already strictly limit the applicability of pre-existing clauses, stemming from the HIPAA reforms in the late 90's. The worst abuses by insurance companies take place in the individual market.