So you think your teenagers are having sex? New research from the United States may surprise you.

A US government report released this week has found fewer than half of American teenagers are sexually active, far fewer than during the late 1980s.

The findings are based on the National Survey of Family Growth conducted between 1988 and 2013.

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The survey examined national estimates regarding contraceptive use, sexual activity and childbearing among 2225 US teens aged 15 to 19 years.

The report found a significant decline in sexual activity in 2011-2013 compared to 1988 when six out of 10 boys and five out of 10 girls were sexually active. 

“In 2011-2013, 44 per cent of female teenagers and 47 per cent of male teenagers aged 15-19 had experienced sexual intercourse,” the report by the National Center for Health Statistics said.

“The percentage has declined significantly, by 14 per cent for female and 22 per cent for male teenagers, over the past 25 years.”

When researchers separated the data by age, they found 15-year-olds were the least likely to have had sex (about 15 per cent).

The research found with time came the increased likelihood of more sex with almost two of every three 19-year-olds having had sex at least once.

Contraceptive use significant factor

Figures within the report highlighted the role of contraception with girls who had not used it the first time they had sex, five times more likely to become pregnant by age 17 as girls who had used some kind of contraception.

The report found the Pill was not the contraceptive of choice among teens. Photo: Shutterstock

Declining rates of sexually active teens also coincided with previous research finding a major decrease in the teen birth rate.

Historically, the highest teen pregnancy rate was in 1957 when 96 of every 1000 people were pregnant.

Given American women began using oral contraceptives in the late 1950s, it was not surprising the teen birth rate in 2013 was just 27 per 1000 people.

The report found the contraceptive of choice was condoms, followed by the withdrawal method. Oral contraceptives – which came to Australia in 1961 – were least popular.

“In 2011-2013, 79 per cent of female teenagers and 84 per cent of male teenagers used a method of contraception the first time they had sexual intercourse,” the report said.

“The percentages have not changed over time.”

The use of emergency contraception, such as the “morning-after pill”, climbed from 8 per cent of girls in 2002 to 22 per cent in 2011-2013.