Lead author Stewart Alexander, an associate professor of medicine at Duke Medicine, along with colleagues at Duke, Indiana University School of Medicine, Ohio State University and Purdue University, said annual physical checkups are prime opportunities for doctors to discuss sexual development, sexually transmitted infections and pregnancy prevention.
"It's hard for physicians to treat adolescents and help them make healthy choices about sex if they don't have these conversations," Alexander said in a statement. "For teens who are trying to understand sex and sexuality, not talking about sex could have huge implications."
The researchers gathered audio recordings of annual visits, including camp and sports physicals, for 253 adolescents. The teens, ages 12 to 17, visited pediatricians and family medicine physicians at 11 clinics in North Carolina.
The researchers found physicians brought up sex in 65 percent of visits, with conversations lasting an average of 36 seconds. The other 35 percent of visits did not mention sex.
The study, published in JAMA Pediatrics, found none of the adolescents initiated discussions on sex -- reinforcing the need for physicians to start the conversation.
"We saw that physicians spent an average of 22.4 minutes in the exam room with their patients. Even when discussions about sex occurred, less than 3 percent of the visit was devoted to topics related to sex," Alexander said.
"This limited exchange is likely inadequate to meet the sexual health prevention needs of teens."
The study found when physicians asked them questions about sex, about half of the teens responded to yes or no questions with limited discussion, and just 4 percent of teens had prolonged conversations with their doctors concerning sex, sexuality or dating.
The researchers also found that older teens were more likely to talk about sex in their visits than younger teens, despite the fact that current guidelines recommend doctors start these conversations in early adolescence before teens are sexually active.
"There's a saying that it's always better to have the conversation two years too soon than one day too late," Alexander said. "If you're one day too late, the teens may already be engaging in sexual behaviors that have consequences for them."
Longer visits and confidentiality both raised the chances that sex was mentioned, Alexander said.
"Although adolescents have access to information on sex from a variety of sources, physicians could do more in support of teens' healthy sexual development," Alexander said.
"Initiating conversations demonstrates to adolescents that talking about sex is a normal part of a checkup, and may open the door for more extensive discussions."