“A highschooler informed me yesterday that they were told by a reputable hospital in this area (they conduct sex ed classes) the following “true” story. Boy and girl had sex. Condom was used. Girl became pregnant. Girl had only been with boy and no one else. DNA proved it was not the boys, but another boy that the girl had not been with sexually. The boy apparently had picked up a used condom and then had sex with the girl. Is this possible???”
A: The scenario you describe seems highly unlikely. Sperm can only stay alive in semen a very short time, and once semen is exposed to air, the condition of any sperm in that fluid deterioarates rapidly. While we cannot say it definitely did not happen, the chances of having viable sperm alive to fertilize an egg are very slim.