Thank you for your query at DoctorSpring.com
A lot of studies have been done and theoretically it's been documented that pre-cum may contain viable sperms carrying a small risk of pregnancy. However, till now no such pregnancy has ever been reported secondary to exposure to pre-cum.
So according to recent studies, pre-cum can't cause pregnancy because the researchers have failed to demonstrate any viable sperms in the pre-cum. It is more of a theoretical possibility.
Feel free to discuss further,