This is the first study 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 non-profit research organization.

According to researchers, 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 added.

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

The 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 behaviour.

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.

The study is published in the November edition of the journal Paediatrics.