heres some info

However, even if the male does not cum inside the vagina, during sexual intercourse, the male is very likely to produce a pre-ejaculate, or pre-cum before orgasm

A high risk of pregnancy is always present when a penis enters a vagina without protection. The withdrawal method, which it sounds like your friend used, is not an adequate form of birth control. According to Crooks and Baur, it has a failure rate of 20% (2003, p.296). Namely, 20 out women out of 100 will become pregnant each year when relying on withdrawal. Sperm can be in the pre-ejaculate fluids, so a female can still conceive when using the withdrawal method

http://www.soc.ucsb.edu/sexinfo/?article=f aq&refid=177

This method, called the withdrawal method, AKA pulling out, AKA coitus interruptus, is a totally ineffective method of pregnancy prevention. After a guy is aroused, and during sexual activity, pre-ejaculatory fluid, AKA precum, is secreted from the urethra. The purpose of this fluid is to neutralize the urethra so the sperm can survive. This fluid contains - you guessed it - SPERM! And as we all know, sperm can very well impregnate a woman. While the amount of sperm is considerably less than released during ejaculation, there is still a significant chance of pregnancy. Consider this: An average of 300 million sperm are released during ejaculation. If one tenth of that amount is released in the precum, that's still 30 million sperm, and it takes only ONE to get pregnant, so wrap it up boys! Another interesting fact: A girl who doesn't use protection during sex has a 90% chance of getting pregnant during the first year.

Pre-cum (or pre-ejaculatory fluid) is the liquid that may leak out of a penis when it is erect before intercourse. It does contain sperm, which is why a condom should be put on a penis before any vaginal penetration occurs.

Pre-ejaculate is actually a sort of lubricant, so it has fewer sperm than the actual ejaculate, but more than enough to make someone pregnant because it only takes one sperm.

Most men can't feel the pre-cum coming out because it is a kind of a leak and it also cannot be avoided or controlled. Pre-cum is one reason withdrawing the penis before ejaculation or "withdrawal" is not an effective way to avoid pregnancy.

http://www.pamf.org/FAQ/FAQ/fx=q/id=19/t=a /c=9/a=13/tid=1/kw=1/z=null/faq.htm