A precipitous drop in the US teenage pregnancy rate to record lows was driven by improved use of contraception, a new analysis from the Guttmacher Institute found.

“There was no significant change in adolescent sexual activity during this time period,” Dr Laura Lindberg, a principal research scientist with the Guttmacher Institute and the paper’s lead author, said in a statement. “Rather, our new data suggest that recent declines in teens’ risk of pregnancy – and in their pregnancy rates – are driven by increased contraceptive use.”

Linberg and her co-authors found that while teenage girls’ sexual activity remained constant from 2007 to 2012, the percentage of sexually active teens who used at least one type of birth control the last time they had sex increased significantly, rising from 78% to 86%.

The researchers found the use of all “highly effective methods”, like the birth control pill or IUD, increased from 2007 to 2009. There was a marginal significant increase in the use of the IUD or implant from 2007 to 2009 and in use of the pill overall. There were non-significant increases in condom use and withdrawal, while use of the ring or patch declined significantly over the 2007 to 2012 period.

The changes in contraceptive use resulted in a 28% decline in pregnancy risk index from 2007 to 2012. Not only did improvements in contraceptive use drive that entire decline, but they were also responsible for neutralizing a 6% rise in risk over the same period due to increased sexual activity among teens. The pregnancy risk index is a calculation that “summarizes the risk of pregnancy among all adolescent women, estimating the influence of both changes in the level of recent sexual activity and changes in the level of contraceptive risk”, according to the study.

In April, the Guttmacher Institute reported that the national pregnancy rate declined 23% from 2008 to 2011 for women aged 15 to 19, falling from a rate of 68.2 pregnancies per 1,000 women to 52.4. That means about 5% of teens became pregnant in 2011. It was the “lowest rate observed in the last four decades”, they said, with declines across all 50 states and racial and ethnic groups, though some disparities remained. In 2011, they found a rate of 31.3 births per 1,000 teen women, down from 40.2 in 2008, and 13.5 abortions per 1,000 teen women, down from 18.1 in 2008.

The new study used data from the National Survey of Family Growth, a survey conducted by the Centers for Disease Control and Prevention, on sexual activity, contraceptive use and contraceptive failures to estimate the pregnancy risk index for the years 2007, 2009 and 2012.

The authors noted it was important to ensure teenagers’ “access to comprehensive sexuality education that provides medically accurate information about contraception”. They wrote that the percentage of adolescents “who report receiving formal instruction about birth control has declined, while the share receiving only abstinence instruction has increased”. The American Academy of Pediatricians recently urged doctors to fill in the gaps of sexual health education with their patients. They noted that abstinence-heavy education is a concern for doctors when it comes to reducing sexually transmitted infections and unintended pregnancies, as those programs can exclude information about contraceptives.

The internet, the authors suggested, can offer new opportunities for teenagers looking for information on sexual health, and recommend further research to examine that hypothesis. A separate study from last year found a correlation between decline in transmission of sexually transmitted infections and access to high-speed internet.

“Policy discussions should focus on supporting teen contraceptive use generally, including ensuring access to a full range of contraceptive education, counseling and methods,” Heather Boonstra, the Guttmacher Institute’s director of public policy, said in the release.

The Guttmacher Institute’s study used data up until 2012, however, more recent data from the CDC’s Youth Risk Behavior Survey “shows sharp declines in sexual activity among high school students from 2013 to 2015 – after a long plateau from 2001 to 2013”, the authors wrote. “At this point, it is unclear whether these new data represent a new trend or are the result of other factors,” the authors wrote.

Another analysis from earlier this month found that millennials are having less sex than those in previous generations.