MINNEAPOLIS (AP) -- Efforts to engage Minnesota teenagers in pregnancy prevention may be paying off.

Several projects across the state are working with teens to bring pregnancy rates down. Experts say those efforts are working, as the birth rate among Minnesota teenagers has plunged nearly 40 percent in the past two decades.

Mary Jo Chippendale, who follows birth rates for the state health department, tells Minnesota Public Radio some of the more obvious explanations don't fully explain what's happening.

While sex education classes tout abstinence, Chippendale says there hasn't been a big change in sexual activity over the last 10 years. And the abortion rate among Minnesota teens ages 15 to 19 has declined at a similar pace as the birth rate.

Chippendale says the most likely explanation is increased contraception use.