I Am A 33 Year Old Male. Last October I

I am a 33 year old male. Last October I had sex with an ex girl friend. She said she was on birth control, but It turns out that was not true. Taking her claim as truth, I did not use protection. We had fully penetrated sex for 1 hour. I didn't ejaculate during sex. it was about 4 month since I had intercourse before this event. I masturbated the night before (I don't know if this matters, I been researching and there many conflicting theories on the web). After the sex she slowly disappeared from my life once again (besides an occasional text here and there)... Around the date of Dec. 17 (give or take a day or two), I got word she is pregnant. She has not told me, but I believe the source she confided in. It turns out she doesn't not know who the father is (my source told me she was asking about DNA tests during utero).... so the question is... is there a possibility I could be the father? I'm not sure on her number of partners she has during that time span... but it is enough to have her thinking also... I'm just looking to see if I can rule my self out of this scenario... this information I shared with you was enough to cause my source alarm. It has me a little paranoid... and if it is Impossible, I don't want to confront her about it.