Parents, relax. Fewer high school-aged teens are having sex, and when they do, they're most likely using contraception, a new government report found.

Sexual intercourse among teens has declined again after rates stabilized between 2002-2010, according to the National Center for Health Statistics report on teen sexual activity and contraceptive use released Thursday by the Centers for Disease Control and Prevention.

The new study shows that just over 40 percent of boys and girls reported having had sexual intercourse by age 18 — a huge decline from the peak of 1988 when 57 percent of teens between the ages of 15 and 19 reported having had sex.

The new report was conducted year round between 2011-2015, included 4,134 male and female teens, ages 15-19. Participation was voluntary and required parental permission, but responses were anonymous.

These results are in line with a 2016 CDC report that showed a leveling off of teen sex in recent decades. The new survey also found that nearly all teens reported using some method of contraception the first time they had sex, an increase from 98 percent to 99 percent since 2002.

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There is no one reason for the decline in teen sexual activity, but previous studies have credited sex education and popular shows like "Teen Mom" and "16 and Pregnant."

“It is undoubtedly complicated," Joyce Abma, statistician for the National Center for Health Statistics, told NBC News.

Not only are teens waiting to have their first sexual encounter, but they're more likely to use contraception. Female teens who reported having had sex in the past 3 months and used contraception at their last sex, increased to 90 percent between 2011-2015, up 13 percent since 1988.

The increase in contraceptive options, such as birth control patches, implantable devices and IUDs, along with increased use of emergency contraception, are likely a major factor, Abma said.

Public health scientist Beth Renee Marshall agreed there has been progress in reducing risky sexual behavior among teens, but there's more to do.

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“There is no doubt that there has been an increase in comprehensive sexual health education," Marshall, associate director for the Center for Adolescent Health at the Johns Hopkins Bloomberg School of Public Health, told NBC News. "But we have not gone far enough as a society in addressing teen sex or safe sex."

Other notable findings from the CDC study:

A small percentage, 2 percent among female teens and 7 percent of male teens, reported having their first sexual experience with someone they had “just met.” The majority — 74 percent of girls and 51 percent of the boys — reported that they were “going steady” with their partner prior to their first sexual experience.

Nearly three in 10 teens, male and female, had sexual intercourse at least once in the past three months.

Condoms are the most commonly reported use of contraception, with 97 percent use reported by teen females, followed by withdrawal (60 percent), and the Pill (56 percent).

Among teens who reported not having had a sexual experience, the most common reasons ranged from religious or moral reasons to "I haven't found the right person yet" and “I don’t want to get a girl pregnant.”