How Birth Control Works

The ultimate goal of birth control is to prevent sperm from fertilizing a woman's egg. Depending on which birth control method is used, however, this goal is achieved in different ways.

Hormonal Methods

Hormonal methods of birth control include such options as birth control pills and the birth control patch, implant, shot and vaginal ring. Hormonal methods contain hormones (either estrogen and progestin or progestin only) that prevent ovulation and thicken a woman's cervical mucus. Without ovulation, there is no egg for sperm to fertilize. In the event that an egg is released, the thick cervical mucus makes it very difficult for sperm to reach the egg.

Barrier methods of birth control include such options as male and female condoms, the diaphragm and cervical cap, the birth control sponge and spermicide. Barrier methods of birth control work by physically or chemically blocking sperm from reaching a woman's egg. Male condoms are fitted over the penis and stop sperm from entering a woman's vagina; other barrier methods are inserted into the vagina in such a way that they prevent sperm from entering a woman's cervix.

The IUD is a T-shaped device that is placed inside the uterus. There are two types of IUDs: the copper IUD, which is coated with copper, and the hormonal IUD, which releases progestin. Both types prevent pregnancy by impairing the ability of sperm to reach a woman's egg. The hormonal IUD may also suppress ovulation and thicken cervical mucus.

Sterilization in women involves cutting, tying or sealing a woman's fallopian tubes. When the tubes are blocked, there is no path for sperm to reach a woman's eggs or for an egg to make its way to the uterus. Sterilization in men involves a vasectomy, a procedure in which the tubes that carry sperm to the penis are surgically cut or blocked. After about 3 months, a man's semen will no longer contain sperm, making him incapable of fertilizing a woman's egg.

Fertility awareness-based methods prevent pregnancy by eliminating unprotected intercourse during a woman's fertile period, the only time of the month during which a woman can get pregnant. The fertile period begins about 5 days before ovulation and lasts until 1 or 2 days after ovulation. By tracking such fertility signs as waking temperature and cervical mucus, users of fertility awareness-based methods can determine the beginning and end of their fertile period and engage in or abstain from unprotected sex accordingly. As long as sex only occurs outside of the fertile period, there will be no egg available for sperm to fertilize.

Withdrawal, or the pull-out method, is a method of birth control in which the man removes his penis from the woman's vagina prior to ejaculation. Withdrawal is usually considered to be unreliable, since it is difficult to perform perfectly and because in some cases sperm can escape from the penis prior to ejaculation. When done correctly, however, withdrawal does greatly reduce the likelihood of pregnancy because it eliminates or greatly reduces the amount of sperm that is allowed to enter the vagina and fertilize an egg.