By Victoria Knight

CNN

(CNN) -- American teens' sex habits and contraceptive use haven't changed much over the past decade, according to a new report from the National Survey of Family Growth, which is administered by the United States Centers for Disease Control and Prevention.

Since 1988, the CDC has been tracking the sexual activities and behaviors of US teens age 15 to 19. The latest numbers from the report released Thursday involved information gathered in interviews with 4,134 teens from 2011 to 2015.

In that time period, 42% of female teens and 44% of male teens reported having had sex at least once, a 1% decrease for females and a 2% increase for males over the previous four years, spanning 2006 to 2010. These differences are not statistically significant.

However, there was a significant decrease in teens who reported having sex in 2011 through 2015 compared to those who reported doing so in 1988. Contraceptive use has also significantly increased over the years. Ninety percent of females now report using contraceptives, compared with 80% in 1988. Males also reported more contraceptive use, from 84% in 1988 to 95% from 2011 to 2015.

Compared with the 2006-2010 report, the latest survey found that reported contraceptive use increased from 86% to 90% in females and 93% to 95% in males, respectively. But these rate differences were also not statistically significant.

The report also found that condoms, withdrawal and the birth control pill were still the most commonly used forms of birth control, with percentages staying steady over the years.

Aligned with these results, the rates of teen pregnancy and births in the US have been steadily decreasing since the early 1990s. In 2015, a historic low of 22.3 births per 1,000 teens was recorded.

Joyce Abma, lead author of the report and a demographer at the CDC, said it's important to understand these trends because teen pregnancy and sexually transmitted infections are public health issues.

"Teen sexual activity and contraceptive use are the direct mechanisms that lead to teen pregnancy" and sexually transmitted infections, Abma said. "So knowing how prevalent, how common, those behaviors are and how they differ according to different subgroups, demographically, helps policy makers and practitioners know where and how to apply intervention."

The CDC survey is conducted annually and involves face-to-face interviews in participants' homes. Teens' responses are gathered in complete privacy. And the questions have not been changed since the survey first asked teens about their sexual activity and contraceptive use in 1988.

Nicole Cushman, executive director of Answer, a national organization that provides sex education training to teachers and resources to young adults, said the survey results are more good news for teens.

"This new data really confirms the continuation of trends that we've been seeing for many years now in teen sexual health," she said. "My take-away message from these trends over the years is that young people are doing a great job at making responsible decisions about their sexual health. I think it really shows that when we equip young people with the knowledge and the skills to protect their sexual health, they're capable of making decisions best for them."

But Cushman also thinks there may be room to expand the scope of questions on the annual surveys.

"Very often, when we look at reports like this, we get focused on the clinical details around pregnancy prevention and STD prevention. And those are certainly important topics," she said. "But when we work with actual teens, what they often remind us of is that these behaviors take place in the context of relationships. And teens really are concerned with the emotional aspects of those relationships. So that's something we need to consider when crafting our sex ed and public health programs."