Precum is a liquid discharge from the penis that occurs during sexual arousal, before ejaculation. While not all precum contains sperm, and thereby the ability to cause a pregnancy, some precum does contain sperm. This depends on a number of factors, a main one being when the man’s last ejaculation was.
There are countless anecdotal reports of pregnancy occurring without there having been any ejaculation inside of the vagina. So how is this possible? There are a number of possibilities for pregnancy without a direct ejaculation, including sperm being present in precum, which is pre-ejaculatory fluid, or urine. So just how likely are these kinds of pregnancies?
A 2016 J Med Thai study found that sperm is found in precum in a shockingly higher number than most people would guess. The study states; Actively mobile sperm were found in 16.7% (7/42 cases) of the pre-ejaculatory penile secretions of subjects whose sperm counts were 2 in 2 cases, 3 in 3 cases and 4 per high power field in the other 2 cases of positive sperm. Semen analyses were normal in 41/42 volunteers (97.6%); there was one case of oligospermia. Actively motile sperm were discovered in the pre-ejaculatory fluid of 16.7% of healthy men.
This means that nearly one in six men should contain actively viable sperm within their precum, though as we will find out, other studies have shown much higher numbers, some showing that up to 41% of study participants have sperm in their precum (1).
Knowing that precum can contain sperm, is it enough to actually fertilize an egg?
Observing the fact that precum contains sperm isn’t alone enough to conclude that precum causes pregnancies at a measurable rate. An appropriate sperm count is needed to reliably fertilize an egg. A 2010 Cambridge study looked into how viable the sperm in precum is. The study found that 37% of men had precum containing a “reasonable proportion” of sperm;
“This study was designed to establish whether motile spermatozoa are released with pre-ejaculatory fluid and whether this fluid therefore poses a risk for unintended pregnancy.
Forty samples of pre-ejaculatory fluid were examined from 27 volunteer men. Samples were obtained by masturbation and by touching the end of the penis with a Petri dish prior to ejaculation. Eleven of the 27 subjects (41%) produced pre-ejaculatory samples that contained spermatozoa and in 10 of these cases (37%), a reasonable proportion of the sperm was motile.
The volunteers produced on up to five separate occasions and sperms were found in either all or none of their pre-ejaculatory samples. Hence, condoms should continue to be used from the first moment of genital contact, although it may be that some men, less likely to leak spermatozoa in their pre-ejaculatory fluid, are able to practice coitus interruptus more successfully than others (2).
While sterile urine from the bladder does not contain sperm, urine can pick up sperm on its way out. Sperm from previous ejaculations can remain in the urethra for several hours after ejaculation.
The results showed that none of the 10 participants had sperm in their urine samples prior to ejaculation. The average sperm concentration was 50.1+/-25.8 million/ml. After a time span of 30 min 59.5% of the first fractions of PEU samples were sperm positive, after 2 and 4h still 70%, and after 5h sperm were no longer detected. The last motile spermatozoa could be found after 4.5h. It seems that remaining sperm in the urethra are washed out with the first micturition in the majority of fertile men, however, the conclusion as to whether sperm findings >5h after ejaculation are improbable needs to be confirmed by further investigations (3).
Knowing this sperm in urine timeline, it’s safe to assume that if you’re not trying to get pregnant it would be a good idea to use a condom if you’ve already ejaculated that same day.
Precum is made mostly of water, plasma, and mucus (a lubricating substance). It is generally not as thick as semen. It contains around 20 calories, and is made up of small amounts of essential nutrients including Calcium, Citrate, Fructose, Glucose, Lactic Acid, Magnesium, Potassium, Protein, and Zinc. Precum and semen contain nutrients because they travel a massive distance in the vagina while attempting to fertilize an egg (4).
Since precum is mostly water and a few common nutrients, it should be safe to eat the precum of a healthy man. The main risk when consuming precum or semen is STDs like herpes, syphilis, and gonorrhea, which can also be contracted just from oral sex alone. If you or your partner want you to swallow precum or semen, you can ask for proof of a recent STI screening.
Keep in mind that HPV is undetectable in men. If you’re worried about a possible semen allergy, you can put a sample of your partner’s semen on your arm and watch for a reaction.