http://www.sexetc.org/faq/pregnancy/992First site I found relating to this topic.
It's possible, but not likely.
Pre-cum or pre-ejaculatory fluid is released when a guy gets an erection. It cleans out the inside of the urethra, which is the tube that carries semen and urine out of the penis.
The fluid makes the urethra less acidic and gives the sperm a better shot at surviving the trip from the guy's testicles to the girl's fallopian tubes. There's usually NO sperm in pre-cum fluid.
Not sure if its right, but it kinda goes along with what i thought so its good enough for me...