It seems like common sense, right?    We don't allow cigarettes on TV because the risk to impressionable younger people is greater than it is with adults.    Adolescents who have high levels of exposure to television programs that contain sexual content are twice as likely to be involved in a pregnancy over the following three years as their peers who watch few such shows, according to a new RAND Corporation study.

The study, published in the November edition of the journal Pediatrics, is the first to establish a link between teenagers' exposure to sexual content on TV and either pregnancies among girls or responsibility for pregnancies among boys. 

"Adolescents receive a considerable amount of information about sex through television and that programming typically does not highlight the risks and responsibilities of sex," said Anita Chandra, the study's lead author and a behavioral scientist at RAND, a nonprofit research organization. "Our findings suggest that television may play a significant role in the high rates of teenage pregnancy in the United States."

Researchers from RAND Health say that exposure to sex on television may influence teen pregnancy by creating the perception that there is little risk to engaging in sex without using contraceptives and accelerating the initiation of sexual intercourse.

"The amount of sexual content on television has doubled in recent years, and there is little representation of safer sex practices in those portrayals," Chandra said. "While some progress has been made, teenagers who watch television are still going to find little information about the consequences of unprotected sexual practices among the many portrayals promoting sex."

She said that the findings hold implications for broadcasters, parents and health care providers.

Broadcasters should be encouraged to include more realistic depictions of sex in scripts and to portray consequences such as pregnancy and sexually transmitted diseases. Parents should consider limiting their children's access to programming with sexual content and spending more time watching programs with their children so they can explain the consequences of sex. Pediatricians should ask adolescents about their media use and discuss with them both contraception and the consequences that may accompany sexual activity.

The new findings are from a RAND research project that previously linked viewing of TV programs with sexual content with earlier initiation of sexual intercourse and other sexual activities. 

The RAND study is based on a national survey of about 2,000 adolescents aged 12 to 17 who were recruited in 2001 and asked about their television viewing habits and sexual behavior. The participants were surveyed again in 2001 and in 2004. The latest analysis is based upon results from about 700 participants who had engaged in sexual intercourse by the third survey and reported their pregnancy history. 

Information about television viewing habits was combined with the results of a separate analysis of television programs to determine the frequency and type of sexual content the adolescents were exposed to during their TV viewing. 

Researchers focused on 23 programs popular among teenagers that were widely available on broadcast and cable television, and contained high levels of sexual content (both depictions of sex as well as dialogue or discussion about sex). The shows included dramas, comedies, reality programs and animated shows. 

RAND researchers found several other factors, in addition to TV viewing, that influenced whether adolescents were likely to experience a pregnancy. Adolescents living in a two-parent household had a lower probability of pregnancy, while girls, African-Americans and those with more problem behaviors such as discipline problems were more likely to experience a pregnancy. Youths who intended to have children early also were more likely to experience a pregnancy.

Chandra said future research topics should include whether inconsistent contraceptive use may help to explain the relationship between exposure to sex on television and pregnancy. 

"Television is just one part of a teenager's media diet that helps to influence their behavior," Chandra said. "We should also look at the roles that magazines, the Internet, and music play in teens' reproductive health."

Although the teenage pregnancy rate in the United States has declined sharply since 1991, the nation still has one of the highest teen pregnancy rates among industrialized nations. Nearly 1 million young women become pregnant each year, with the majority of these pregnancies unplanned. Research has shown that young mothers are more likely than others to quit school, require public assistance and to live in poverty.