Is the withdrawal method an effective contraceptive choice? Do you need to be worried about an unwanted pregnancy if you and your partner had 10-second unprotected intercourse? Is it at all possible, even theoretically, for pregnancy to result from dry-humping because precum might somehow seep through your clothes and into all the wrong places?
What Is 'Precum' Or Pre-Ejaculatory Fluid?
Pre-ejaculatory fluid or pre-ejaculate, colloquially referred to as "precum", is a fluid released from the penis during sexual activity. Precum is believed to come from the Cowper’s glands and the Glands of Littre, but that probably isn't interesting to you right now — what you do want to know is that precum is released spontaneously, that it helps facilitate pleasurable sexual intercourse in much the same way vaginal discharge does, and that men have zero control over its production. In fact, they don't even feel it being released. 
Can You Get Pregnant From 'Precum'?
Fortunately for those folks who want kids and those who simply want humans to keep being around, the average ejaculate contains millions of sperm cells. Men who have 39 million sperm cells per ejaculate are only barely considered to have viable sperm counts , and the average ejaculate features around 100 million sperm. Out of that 100 million, only about 10 million make it past the cervix, only about a million make it into the upper uterine tract, and a meager 100,000 get as far as the fallopian tubes. 
What's more, one study shows that precum doesn't contain any sperm most of the time, and that if it does, most of the sperm is immobile (that is, can't "swim").  We'll add that that particular study happened to refer to HIV-positive men, and that another study contradicted its findings.
It's worth quoting part of that study:
Although our pre-ejaculatory samples often contained sperm with equivalent concentration and motility to what would be regarded as fertile in ejaculatory samples, the actual number of sperm in the pre-ejaculates was very low. We are unable to say how this finding might translate into the chances of pregnancy if these samples of pre-ejaculate were deposited in the vagina except that the chances would not be zero. 
What does that mean, in real terms, for those who don't want to get pregnant and don't want to get their partners pregnant? Let's look at that now.
Is The Withdrawal Method An Effective Contraceptive Choice?
Almost 60 percent of US women aged between 15 and 44 have ever used the withdrawal method (or pull-out method) as a form of contraception . If you're wondering if you should use the withdrawal method as your chosen birth control as well, it's important to know that there's the pull-out method and the pull-out method:
- You could just have sex whenever you feel like it and have the male partner pull out before ejaculation.
- Some couples carefully monitor the female partner's menstrual cycle to find out when she is in her fertile window, and adjust their sex life accordingly.
The latter method is also referred to as "natural family planning", and couples who practice it monitor ovulation by charting basal body temperature and looking at the consistency of cervical mucus. They then either avoid sex altogether during the woman's (presumed) fertile days, or they use condoms only during those days. They use the withdrawal method the rest of the month.
The efficacy of every user-dependent contraceptive method depends on a user's ability to follow its instructions perfectly, of course. The combined oral contraceptive pill has a failure rate of about 0.1 percent when it's used perfectly, for instance, but because most people aren't perfect, research indicates that the actual failure rate is much closer to 8.5 percent. 
To get back to precum, the sperm that might be lurking in there, and the less official way of practicing withdrawal, just pulling out before the male partner reaches climax without paying any attention to the female partner's menstrual cycle, well, we can only repeat what the study above said. Your chances of getting pregnant aren't zero even when you use the really thought-out form of the pull-out method as you have already seen above, so they're definitely not going to be zero if you have no clue when you are fertile, or your girlfriend is.
The Bottom Line
Is it even theoretically possible to get pregnant from precum released during dry-humping? I'd have to go with "no" on that one. Do you have to worry about pregnancy after 10-second intercourse? Not really. (You may want to look out for sexually transmitted diseases, though.) Is the withdrawal method an effective contraceptive choice? That depends on how you practice it.
If you want to have satisfying sexual intercourse without worrying about pregnancy or monitoring your fertility, you may want to choose a more user-friendly contraceptive method, like an intrauterine device or Depo-Provera.