I recently slept with a friend twice in the same night. We had protected sex (condom). The sex took place 4 days after her menstrual cycle started.
About 10 days after her cycle started, she slept with another guy. They had unprotected sex, and he ejaculated into her. She took Plan B within 12 hours of sexual intercourse.
She subsequently missed her next period, and is pregnant. What is the likelihood I could be the biological father? We slept together early in her cycle, and used protection. They were closer to her peak fertilization dates, but the failure of the Plan B is what has me concerned. I know it can fail, but the numbers are low.