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Here's what has to happen for pregnancy[br]to occur after sexual intercourse.

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Sperm must swim up the vagina,

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through the cervical opening,

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upwards through the uterus,

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and into one of the two fallopian tubes.

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If an egg, released during [br]that month's ovulation, is in the tube,

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one sperm has a chance to fertilize it.

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Contraceptives are designed[br]to prevent this process,

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and they work in three basic ways.

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They block the sperm,

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disable sperm [br]before they reach the uterus,

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or suppress ovulation.

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Block is the simplest.

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Male and female condoms prevent[br]sperm from coming into contact

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with the vaginal space.

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That barrier is also why they,[br]unlike other contraceptive methods,

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are able to prevent transmission[br]of certain sexually transmitted diseases.

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Meanwhile, the diaphragm, [br]cervical cap, and sponge

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work by being placed over the cervix,[br]barricading the entrance to the uterus.

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These contraceptives are sometimes[br]called barrier methods

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and can be used with spermicides,

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an example of [br]the second category, disable.

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A spermicide is a chemical [br]that immobilizes and destroys sperm.

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Today's spermicides come as foam,[br]cream, jelly, suppositories,

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and even a thin piece of translucent film[br]that dissolves in the vagina.

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These products can be inserted directly[br]into the vagina before intercourse,

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or can be combined with block methods,[br]like a diaphragm or condom,

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for added proection.

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The third category [br]for preventing pregnancy

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works by suppressing the action of an egg[br]maturing in the ovary.

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If there isn't an egg available [br]in the fallopian tube,

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there's nothing for sperm to fertilize.

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Hormonal contraceptives,

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including the pill, the patch, [br]the Depo shot, and the vaginal ring

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all release synthetic versions of various[br]combinations of progesterone and estrogen.

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This hormone cocktail [br]suppresses ovulation,

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keeping the immature age [br]safely sequestered in the ovary.

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Synthetic progesterone also has a block[br]trick up its sleeve.

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It makes cervical mucus too thick and[br]sticky for sperm to swim through easily.

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There are other contraceptives that[br]use multiple approaches at the same time.

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For example, many IUDs,[br]or intrauterine devices,

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contain synthetic hormones [br]which suppress ovulation.

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Some also contain copper,

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which disable sperm while also making[br]egg implantation in the uterus difficult.

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Block, disable, or suppress.

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Is one strategy better than the other?

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There are differences, but a lot of it[br]has to do with how convenient

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and easy it is to use [br]each contraceptive correctly.

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For example, male condoms would be[br]about 98% effective

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if everyone used them perfectly.

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That 98% means if 100 couples correctly[br]used condoms for a year,

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two women would get pregnant.

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But not everyone uses them correctly,[br]so they're only 82% effective in practice.

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Other methods, like the patch and pill,[br]are 99% effective

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when they're used perfectly.

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But in practice, that's 91%.

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Spermicide is only 85% effective,[br]even with perfect usage,

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and just 71% effective with typical usage.

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Another important consideration in the[br]choice of contraceptives are side effects,

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which almost exclusively effect women[br]rather than men.

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Hormonal methods in particular[br]can cause symptoms like headaches,

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nausea,

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and high blood pressure,

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but they vary from woman to woman.

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That's why these methods[br]require a prescription from a doctor.

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The choice of contraceptive method[br]is a personal one,

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and what works best for you now[br]may change later.

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Scientists also continue to research[br]new methods,

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such as a male pill that would[br]prevent sperm production.

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In the meantime, [br]there are quite a few options

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to block sperm,

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disable them,

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or suppress eggs[br]and keep them out of reach.