According to a new study by the RAND Corporation, adolescents who have high levels of exposure to television programmes 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.

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 behavioural 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 programmes 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 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 2002 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 programmes to determine the frequency and type of sexual content the adolescents were exposed to during their TV viewing.

Researchers focused on 23 programmes 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 programmes and animated shows.

RAND researchers found several other factors, in addition to TV viewing, that influenced whether adolescents were likely to experience a pregnancy. They also noted that adolescents living in a two-parent household had a lower probability of pregnancy.