13-1405. Sexual conduct with a minor.
A. A person commits sexual conduct with a minor by intentionally or knowingly engaging in sexual intercourse or oral sexual contact with any person who is under eighteen years of age.
So, yes, you could be charged. You are over 18 and she is under. Her pregnancy is obvious proof of sexual intercourse and a DNA test would prove that the intercourse was with you. Whether a prosecutor would actually file charges in your circumstances, I cannot say. If you are contacted by law enforcement, you should get an attorney immediately.