Crocodile dung and honey. What could they possibly have in common? In the past, both were mixed with other ingredients and inserted into the vagina to prevent pregnancy. It sounds weird, but the strange concoctions worked. A woman's body temperature melted the crude suppository into a barrier over the cervix. This is called a pessary. And believe it or not, pessaries are used today. (Of course, they're not made of crocodile dung.)

Millions of women follow in their ancient ancestors' footsteps when they use contraceptive foams. This method of birth control not only forms a barrier against the cervix, but also kills sperm with the addition of a spermicidal chemical.

If you follow the directions and use foam each time you have intercourse, research places your risk of getting pregnant at about 80 percent. And you have the power to increase those odds by using condoms, according to Susan Dantoni, M.D., an obstetrician and gynecologist in Geneva, N.Y. Many sources put the effectiveness of using foam and condoms together at about 95 percent.

The foam comes with an applicator. While lying down, a woman inserts the applicator far up into the vagina and pushes a plunger to release the foam. The goal is to deposit the foam as close to the cervix as possible.

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