The Math of Teenage Sex

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America's left and right are once again at odds, this time over a plan at the King Middle School in Portland, Maine, to make birth control pills available without parental approval to girls as young as 11. The school committee voted 7 to 2 in favor of the plan last Wednesday.

You know kids are having sex early these days when contraception pills could be marketed as Flintstone Chewables.

One side asks: Is it moral to sanction early sexual activity? The reality, the other side counters, is that teenagers are sexually active and the burden of unwanted pregnancies is too high.

Expect no resolution anytime soon. Perhaps middle ground could be reached, however, if we focus on the wonderful opportunity this issue provides us to improve our teenagers' dismal math skills.

If you do the math—worthy of an SAT prep course, with fractions and large numbers—you'll find that early sex plus the Pill equals sexually transmitted disease and maybe even pregnancy.

In a perfect world

Oral contraception is a superb method of birth control, more than 99 percent effective if used properly. The chances of a teenage girl using the Pill properly are likely closer to zero, however, making this a rather dicey method to prevent pregnancy. There's no solid data supporting the practicality of getting very young teens on the Pill.

That's math lesson number one for the middle school kids. The concept of 99-percent effectiveness—or 99.7 percent for the combination estrogen and progestin pill, to be precise—is based on perfect use, an unrealistic laboratory dream. For the average woman, who forgets to take the Pill some days, the rate drops to around 90 to 95 percent. For the average teenage girl, who forgets to turn off the hairdryer, the rate is lower yet.

And of course, the Pill does nothing to prevent STDs.

Sex by numbers

According to the Centers for Disease Control and Prevention, 15- to 24-year-olds make up about half of all new STD cases each year, despite representing only a quarter of the sexually active population. That's 9.1 million young folks among the 18.9 million contracting an STD each year.

Here comes math lesson number two. According to the last census, the 15- to 24-year-old bracket was about 14 percent of the U.S. population, which means there are about 42 million adolescents and young adults among 300 million Americans. Nine million cases divided by 42 million people translates to 21 percent, or more than one in five under age 24 with an STD.

More math: Nearly 75 percent of new chlamydia cases and 60 percent of new gonorrhea cases are in this age bracket, according to the CDC. Compared to women in all other age categories, 15- to 19-year-old females have the highest rate of gonorrhea. More than 10 percent of all 15- to 24-year olds have genital herpes. There are TV commercials for herpes, after all, because the STD is so widespread, affecting 45 million Americans.

These and other STDs, such as the human papillomavirus, the most common among young adults, can bring serious consequences, such as infertility and cancer.

Getting an early start

The earlier one becomes sexually active, without a condom and perhaps emboldened by some false idea of the protections offered by the Pill, the greater the risk of contracting an STD.

A girl "sophisticated" enough to seek oral contraception at a health clinic likely has a boyfriend, often older, pressuring her to have sex without a condom, or she is already sexually experienced. Either way, the odds are against her remaining disease free.

Alas, American teenagers don't like math. They like sex. The King Middle School reported 17 pregnancies in four years; the number of miscarriages and abortions are unknown.

Handing out prescriptions for oral contraception is no solution, but coupled with counseling by health professionals who try to dissuade girls from becoming sexually active and who insist on condom use, the plan might have a positive outcome.

Too bad more teenagers can't be like me in high school, homely and sarcastic. Then they would have little chance of having sex.

Christopher Wanjek is the author of the books “Bad Medicine” and “Food At Work.” Got a question about Bad Medicine? Email Wanjek. If it’s really bad, he just might answer it in a future column. Bad Medicine appears each Tuesday on LiveScience.

Christopher Wanjek
Live Science Contributor

Christopher Wanjek is a Live Science contributor and a health and science writer. He is the author of three science books: Spacefarers (2020), Food at Work (2005) and Bad Medicine (2003). His "Food at Work" book and project, concerning workers' health, safety and productivity, was commissioned by the U.N.'s International Labor Organization. For Live Science, Christopher covers public health, nutrition and biology, and he has written extensively for The Washington Post and Sky & Telescope among others, as well as for the NASA Goddard Space Flight Center, where he was a senior writer. Christopher holds a Master of Health degree from Harvard School of Public Health and a degree in journalism from Temple University.