It's fruitless to speculate on statistical chances of pregnancy, because there are so many co-factors. Let's just say that your chances of pregnancy are very high if you don't use effective contraception. And let's not ignore your risk of infection as well. Before exposing yourself to sperm and/or infection, you need to educate yourself regarding effective contraception and risk reduction. Check elsewhere on this site for excellent information and resources. Remember: with great sex comes great responsibility. Have fun and play safe. Dr. J
If you don't want to get pregnant definitely protection because as you know it only takes 1 sexual encounter at the right time to become pregnant. So I would say if you are not ready for the responsibility of taking care of a child then use protection.