The withdrawal method is definitely not a good method of birth control because of it's very high failure rate. (over 27%). However, no medical study or research has to date shown that sperm is normally contained in precum.
This method fails to prevent pregnancy in the follwing ways:
1. Sperm can get into precum if the male has ejaculated earlier in the day, because leftover sperm can mix with precum and impregnante a woman.
2. As a man pulls out and ejaculates, he may get some on the outside of the vagina, close enough for the semen to still get inside and some sperm can reach the egg.
3. The most common way this method fails is that the male cannot properly control when he ejaculates, and doesn't pull out in time.
"Precum, also known as "pre-ejaculate", comes from a part of the male body known as the Cowper's gland or the Bulbourethral gland. The counterpart in the female body is known as Bartholin's glands.
These glands do not manufacture or contain sperm.
Bulbourethral Glands
The paired bulbourethral (Cowper's) glands are small, about the size of a pea, and located near the base of the penis. A short duct from each gland enters the proximal end of the penile urethra. In response to sexual stimulation, the bulbourethral glands secrete an alkaline mucus-like fluid. This fluid neutralizes the acidity of the urine residue in the urethra, helps to neutralize the acidity of the vagina, and provides some lubrication for the tip of the penis during intercourse.
They are homologues of bartholin's glands in the female.
bulbourethral glands
Two glands in the substance of the sphincter of the urethra, just posterior to its membranous part and located near its origin. They are homologues of bartholin's glands in the female. They supply mucus to the urethra during sexual intercourse to assist in the lubrication of coitus.