How effective is withdrawal as a birth control method?In this method, also called coitus interruptus, the man withdraws his penis from the vagina before ejaculation. In theory, fertilization is prevented because the sperm don't enter the vagina.
Withdrawal has a high failure rate, in part because even if the man is able to withdraw on time, pre-ejaculatory fluid may contain traces of sperm. This pre-ejaculatory fluid can enter the vagina before full ejaculation and is much harder to anticipate and control. Also, withdrawal doesn't provide protection from STDs, including HIV. Infectious diseases can be transmitted by direct contact with surface lesions and by pre-ejaculatory fluid.
Adapted from the United States Office on Women's Health in the Department of Health and Human Services.