What is the percentage rate of a women getting pregnant from precum?

Use contraception: Not sure the exact percentage is known. However, sperm is present in pre-cum, which is sufficient to result in pregnancy. If trying to avoid pregnancy, best to use some sort of contraception (condoms, birth control pill, etc.).

Don't know %: Most studies have shown low levels of sperm or no sperm in pre-ejaculate with sperm not being motile (however, don't know how promptly samples were examined). 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/

Use condoms: Use condoms!!! #1) Then this question would be irrelevant. #2) Then you will lower your risk of sexually transmitted disease. If no condom, then have him keep his pants on and zipper zipped!