another truth. Precum, all though it's job is to sterilize the canal that the semen will run down, also sometimes hold a small amount of semen itself and can cause pregnancy. It's rare but it happens
Study 1
PIP: A study in Boston, Massachusetts, and another study in New York City examined samples of pre ejaculate fluid from HIV seropositive and HIV seronegative men to determine whether HIV was or was not present in pre ejaculate fluid. The researchers found macrophages and CD4 lymphocytes in most samples, indicating that HIV was present. The more significant finding, however, was that most pre ejaculate samples did not contain any sperm and those that did had only small clumps of a very small amount of sperm which seemed to be immobile. A larger study is needed to verify these results. If these results are confirmed, they may dispel the myth that pre ejaculate fluid contains sperm. An ongoing WHO/USAID study shows that the pregnancy rate caused by men with 3 million sperm/ml/ejaculation is very low; fertility clinics consider men with a sperm count of no more than 5 million/ml to be infertile, particularly if is there is low motility. The average ejaculation has about 100 million sperm/ml, but about 10 million sperm pass through the cervical mucus, about 1 million make it to the top of the uterine tract, and just about 100,000 sperm reach the fallopian tubes. Thus, only a couple of sperm, assuming motility, would reach the fallopian tubes in the case of the pre ejaculate samples with some sperm, which tended to be immobile (sperm levels only in the 1000s). Thus, the probability of pregnancy is very love if pre-ejaculate fluid enters the vagina. Pre-ejaculate fluid of 6 of the 9 HIV seropositive donors in Boston and 6 of the 14 HIV seropositive donors in New York contained HIV, regardless of symptom status or antiretroviral therapy status. Thus, the risk of HIV transmission may be higher than unplanned pregnancy, so people should use condoms before the penis enters the vagina, mouth, or anus. -PMID: 12286905 [PubMed - indexed for MEDLINE] .
Study 2
Journal of Assisted Reproduction Genetics, 2003 Apr;20(4):157-9. Zukerman asked "Does preejaculatory penile secretion originating from Cowper's gland contain sperm?" - conclusion: "Preejaculatory fluid secreted at the tip of the urethra from Cowper's gland during sexual stimulation did not contain sperm and therefore cannot be responsible for pregnancies during coitus interruptus."
Studies 3 and 4
Here's another two studies that were studying the HIV viral load in pre-ejaculate and incidentally showed that there isn't sperm:
Ilaria G, Jacobs JL, Polsky B, Koll B, Baron P, MacLow C, Armstrong D, Schlegel PN. Detection of HIV-1 DNA sequences in pre-ejaculatory fluid. Lancet 1992;340:1469.
Pudney J, Oneta M, Mayer K, Seage G, Anderson D. Pre-ejaculatory fluid as potential vector for sexual transmission of HIV-1. Lancet 1992;340:1470.
What these scientific findings suggest is that precum either does NOT contain sperm AT ALL, or that there is so little that the chances of pregnancy are very VERY low. The chances are not eliminated but they are so low that becoming pregnant from pre-cum easily becomes urban myth.
Also remember, if the man has ejaculated before you have intercourse again, the chances are increased for conception because semen will still be left within the penis itself and further along the male reproductive organ.