I'm an 18 year old male in Tennessee and I believe I may have gotten my 16 year old girlfriend pregnant

I am assuming that there was no force used in the relationship and this was totally by consent. The offense of statutory rape covered involves an age element of the difference between you and your girlfrient. Because of your close ages it appears that you are not covered by the statutory rape statute. I have also reviewed the child abuse and  sexual battery statutes and they do not seem to apply either. Having said this, this does not mean that the mother might, as you said, try to start some sort of criminal prosecution against you. If she tries to do this, then it would be up to the DA in the county where you live to decide what statute, if any, that it thinks that you violated.