It only takes one good swimmer.

By Christina Oehler
Updated June 05, 2019

Junior high sex-ed class made us believe that if a boy so much as sneezed on you, you could get pregnant. And if he managed to get precum in the vicinity of your vagina? Well, you might as well start planning your baby shower.

But now that we're adults, we were curious: What are the odds of pregnancy by precum, really? So we spoke to two sexual health MDs to find out.

Precum, or pre-ejaculate fluid, is the substance that comes out of a man’s penis when he’s sexually aroused but before an orgasm. It’s released from the bulbourethral glands, also known as Cowper's glands—two pea-size glands located between the prostate and the base of the penis. Unlike semen, which is released during ejaculation and contains upwards of 200 million sperm per shot, precum contains barely any viable sperm.

“Most of the evidence leans toward pre-ejaculate containing no sperm, or only very tiny amounts of sperm,” Michael Reitano, MD, physician-in-residence for the men’s health website Roman, tells Health. “What sperm is found [in precum] tends to be poorly formed and immobile. Men are considered infertile if they have too little sperm, so the tiny amounts that may be found in pre-ejaculate are extremely unlikely to result in pregnancy.”

While pregnancy is highly unlikely, it’s not impossible.

“It just takes one good swimmer,” says Amanda Kallen, MD, assistant professor of obstetrics, gynecology, and reproductive sciences at Yale School of Medicine. If your male partner puts his penis inside your vagina even for a moment, it is possible for one hardy sperm in his precum to travel past your cervix and fertilize an egg.

No wonder "pulling out" is such a poor form of birth control. “The pull-out method, if used perfectly, has a failure rate of about 4%," says Dr. Kallen. "But in real life it’s more like 22%."

Even if a guy thinks he's pulled out in time, it doesn't always work out that way. “A man may believe he withdrew before the start of ejaculation, but the timing of an orgasm and ejaculation is not always perfectly coordinated,” says Dr. Reitano. “He may begin to ejaculate a moment before he senses his orgasm. What is released then is not precum, but the actual first small emissions of ejaculation.”

If precum isn't supposed to carry sperm, what's the purpose of it? According to Dr. Reitano, it's a basic fluid that is released to protect sperm from the acid environment of the urethra and the vagina. It also aids in lubrication to some degree.

Precum carries another risk besides a hidden sperm or two. “Precum can transmit sexually transmitted diseases,” says Dr. Reitano. “Precum may not have sperm, but it can easily contain any infectious material a person may carry, and this means the disease can be transmitted to a partner.”

Bottom line: If you want to be truly safe from pregnancy and STIs, wrap that penis up before sex begins—so no precum or ejaculate can get inside you.

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