Yes, pre-ejaculatory fluid CAN contain sperm, which could theoretically result in an unintended pregnancy. However, not all pre-ejaculatory fluid contains sperm. This fluid is made by the prostate, not the testes that produce sperm, and thus contains no sperm on its own. If your partner ejaculated a short while before and hadn't urinated, some sperm from that ejaculation could have been left behind in the urethra and mixed with the "new" pre-ejaculatory fluid. If he hadn't already ejaculated at least once, then the chance that his 'pre-cum' contained sperm is highly unlikely.