Does pre-ejaculate contain sperm? if so, is there a way to prevent it from containing it?

It can: Yes it can and you cannot change that which is why we dot recommend the withdrawal method for birth control.

It can: Most studies have shown low levels of sperm or no sperm in pre-ejaculate with sperm not being motile. One small study published in 2011 showed that there are some individuals with a high motile sperm count in pre-ejaculate. See: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3564677/ Pre-ejaculate