But while talks with parents may be one important factor in helping youth make safer choices, it is clearly not the only factor, because the link between parent communication and teen sexual behaviour was relatively small, said lead author Laura Widman of North Carolina State University in Raleigh.
Effect strongest for girls
Parents could talk about other topics that impact risky sexual choices, such as substance abuse, peer pressure, and a lack of communication about safety between dating partners prior to engaging in sex, Widman told Reuters Health by email.
The review included 52 studies with more than 25,000 teens, all including teen reports of communication with one or both parents and measures of safer sex behaviour.
Teens who reported having these conversations with their parents also tended to exhibit safer sex behaviour and were more likely to use condoms or other contraception.
The effect was strongest for girls and for teens who spoke to their mothers, specifically.
There were no significant differences based on the topics parents discussed with their teens, Widman and colleagues reported in JAMA Paediatrics.
"We know that parents tend to communicate more frequently with girls than with boys," Widman said.
"We also know that the messages parents share are more likely to stress the negative consequences of sexual activity, like pregnancy, when they talk with their daughters."
Parents matter too
Parents may need to increase how often they talk with their sons about sex and change the content of the messages surrounding sex that they communicate to boys, she said.
Most teen sex education programmes are aimed directly at the adolescent, including posting information and making condoms available in proximity to them,
said Dr Vincent Guilamo-Ramos of New York University, who co-authored an editorial published with the new results.
Read: Learn to talk about sex
"Those are all terrific and we should keep doing them," but parents matter, too, he told Reuters Health by email.
Other studies have found that parents can help delay teen sexual debut, and this review now supports an influence on contraceptive use as well, he said.
"We want to get parents engaged and communicating on these issues," Guilamo-Ramos said.
Better to wait
Adolescents account for a quarter of sexually active individuals but have half of all sexually transmitted infections, and there are still 600,000 teen pregnancies in the U.S. per year, he noted.
Read: Teen sex stats shocking
Often parents underestimate when their kids are having sex, believing other kids are sexually active, but not their own, he said.
Sex talks should begin early around age 11 or 12, and should stress that it is better to wait, he said.
"A true family based approach is one where parents are getting the information and they decide how to deliver it, as opposed to a one size fits all curriculum," Guilamo-Ramos said.
Parents should stress that the positive things teens hope to gain from sex, like more closeness with a partner, feeling popular or mature, are false expectations, and do not outweigh the dangers of teen pregnancy or STDs, he said. "Many parents are fearful that if they bring the topic up, teens will initiate sexually," but the opposite is true, he said.
"Youth who are not able to talk with their partners about topics like sexual limits, condoms, and STDs are much more likely to engage in risky sex," Widman said.
"When parents model how to have open and honest conversations about sex with their teens, they can help teens learn how to have similar conversations with their dating partners.