Coitus interruptus

Coitus interruptus, also commonly called the withdrawal method, is an unreliable method of contraception in which, during sexual intercourse, the man removes his penis from the woman's vagina just before his orgasm. That way, the ejaculation of semen is not in the vagina but elsewhere.

Used by itself, this method can be very unreliable, because pre-ejaculate may contain spermatozoa (sperm). Pregnancy is also possible if semen contacts the female vulva. Additionally, not everyone is able to note the arrival of orgasm in a timely manner, and interrupting just at climax can be psychologically difficult, as it goes entirely against instincts and reflexes all designed to encourage procreation by encouraging ejaculation to occur deeply within the vagina.

The advantage of coitus interruptus is that it can be used by people who have religious objections against other methods of contraception, and that it requires no artificial devices. A man in a committed relationship might also enjoy the fact that his female partner is not subjecting herself to artificial hormones. The disadvantage, as stated, is that it can be extremely unreliable.

Also known as "the natural method" and "pulling out".

According to a widely circulated joke, the Ob. Gyn. nurse argot term (or slang term) for a woman relying on "the natural method" is "mother". However, being educated about different forms of natural methods and combining them can be as effective as the pill. You can read more about combining methods from the Taking Charge of Your Fertility: The Definitive Guide to Natural Birth Control and Pregnancy Achievement by Toni Weschler.

From Emory University, withdrawel has a typical failure rate of 19%. However, for the couples that use this method correctly, the failure rate is 4%. http://www.emory.edu/WHSC/MED/FAMPLAN/withdrawal.html