The reason that there are many forms of birth control devised is that the “natural” one is famous for failure.

The natural one is the rhythm method, relying upon the female to calculate when she is most like to become pregnant and avoiding sex at that time.

The failure rate is placed at 25% by reproductive experts and is the same rate quoted in the full story below from the AP.

This story also says that the number of teen-aged, sexually experienced girls  using the rhythm method increased from 11% in 2002 to 17% in the Centers for Disease Control and Prevention’s latest survey.

AP

“A growing number of teen girls say they use the rhythm method for birth control, and more teens also think it’s OK for an unmarried female to have a baby, according to a government survey released Wednesday.

“The report may help explain why the teen pregnancy rate is no longer dropping like it was.

“Overall, teenage use of birth control and teen attitudes toward pregnancy have remained about the same since a similar survey was done in 2002.

“But there were some notable exceptions in the new survey by the Centers for Disease Control and Prevention. About 17 percent of sexually experienced teen girls say they had used the rhythm method — timing their sex to avoid fertile days to prevent getting pregnant. That’s up from 11 percent in 2002. “(Emphasis added)

Source: AP, June 2, 2010