What is the possibilities of getting a female pregnant with precum if any leaks out?

Yes, ...: It's possible and that is how accidental pregnancy takes place although pre-cum contains much less sperms than semen. Besides, remember: No known contraceptive measure has ever offered a 100% guaranty; so, always exercise due diligence and vigilance for contraception if reproduction is not why you have sex. For safer sex, seek more counseling from PCP or gyn-doc timely. Best wish ...

See below: If you want to avoid getting her pregnant,either ask her to get on birth control pills &/or use condoms.

Difficult to say...: Studies of pre-ejaculate are mixed. Some studies showed no sperm, and other showed mixed amounts containing over a million sperm. If a male has ejaculated earlier in the day there could also be sperm in the urethra "leftover" which could mix with the pre-ejaculate. Irregardless, if you are trying to prevent pregnancy, you should always wear a condom from the start to finish.