How Birth Control Methods Prevent Pregnancy

How Pregnancy Happens

Ovulation is usually at the midpoint of a woman's menstrual cycle. It takes place when the right mixture of hormones reach a certain point. Pregnancy occurs when a woman ovulates and releases an egg from the ovaries. The egg than travels down through the Fallopian tubes, where it may possibly be fertilized if met by sperm from a male's ejaculate. A fertilized egg moves into the uterus, where it becomes implanted into the lining of the uterus and begins to produce hormones supporting its development. Contraception works by affecting: a woman's ability to ovulate and produce an egg; the ability of an egg and sperm to meet; sperm's motility; the ability of a fertilized egg to remain attached to the uterus wall; or in a combination of the above.

How Sterilization and Hormonal Methods Work

Aside from abstinence, the most effective birth control method is sterilization. A vasectomy prevents sperm from leaving a man's reproductive organs. A tubal ligation ("getting tubes tied") prevents an egg from leaving a woman's reproductive organs. If the necessary components (sperm and egg) are not able to meet, there is no way pregnancy may occur.

Hormonal methods such as: oral contraceptives (aka "The Pill"), Depo-Provera ("The Shot"), Ortho Evra ("The Patch"), Nuva Ring, Plan B and Implanon (the implant) work to control a woman's hormones that enable her to ovulate. These approaches contain estrogen and/or progestin and mainly work by keeping a woman from releasing a mature egg. Hormones may also prevent pregnancy by making the wall of the uterus more impervious to a fertilized egg so it cannot implant itself or by thickening cervical mucus making sperm less motile. An Intrauterine Device or IUD gives off progestin and can be considered a hormonal method, but it also works by scraping the uterus wall keeping an egg from implanting. Currently, there is research to produce a hormone method for men.

How Barrier and Behavioral Methods Work

Barrier methods such as male/female condoms, diaphragms, cervical caps and sponges prevent pregnancy by blocking the sperm from entering the uterus. If a sperm cannot reach the uterus, it can't fertilize an egg. Barriers are often used with spermicide that works by disabling the mechanism that enables sperm to move. Immotile sperm have a very difficult time of swimming to an egg and fertilizing it. Lastly, there are behavioral methods such as fertility awareness planning, breastfeeding or withdrawal that are also used but not usually as effective. These methods work by limiting contact of the vagina and penis, or by judging the timing of when a woman may ovulate or a man may ejaculate. Other behavioral methods such as outercourse, oral sex and anal sex effectively work by completely preventing vaginal penetration of the penis.