It's possible but unlikely. It's based on when you ovulate, which for most woman is about 10-14 days after their period. Sperm can only live in the body for up to 7 days, so by the time you (probably) ovulate, it would more than likely be dead and won't fertilize an egg. But, you should probably wear a condom or get on BC if you want to avoid getting pregnant because the chance, even though it's low, is always there.