CHICAGO - Teen girls who have sex should use IUDs or hormonal implants - long-acting birth control methods that are effective, safe and easy to use, the nation's most influential pediatricians group recommends.

In an updated policy, the American Academy of Pediatrics says condoms also should be used every time teens have sex, to provide protection against sexually transmitted diseases that other forms of birth control don't provide, and to boost chances of preventing pregnancy.

Condoms alone are the most common birth control choice among teens, but with typical use they're among the least effective methods at preventing pregnancy. Both long-acting methods are nearly 100 percent effective, with lower failure rates than birth control pills, patches and injections, the academy says.

IUDs and hormonal implants cost more, usually hundreds of dollars, because inserting them involves a medical procedure typically done in doctors' offices. But they're less expensive in the long run than over-the-counter condoms or prescription birth control pills, said Dr. Mary Ott, an adolescent medicine specialist and associate pediatrics professor at Indiana University. She is the policy statement's lead author,

Teens have to remember to use pills and condoms consistently. By contrast, IUDs typically work for three to 10 years after insertion, while implants typically last three years.

The new guidance was published Monday in Pediatrics. It echoes 2012 recommendations from the American College of Obstetricians and Gynecologists.

The policy emphasizes that abstinence is 100 percent effective at preventing pregnancy and sexually transmitted diseases and says pediatricians should encourage teens to delay sexual activity "until they are ready." But since many teens don't heed that advice, the policy also says pediatricians need to provide birth control guidance.

IUDs - intrauterine devices - are small, T-shaped devices containing hormones or copper that are inserted into the womb to prevent pregnancy. Hormone-containing birth control implants are matchstick-size plastic rods placed under the skin of the upper arm.

"All methods of hormonal birth control are safer than pregnancy," Ott said.

These include pills, patches and injections.

The academy's new advice updates a 2007 birth control policy that didn't recommend specific methods other than condom use.

For the first time, the new policy addresses obese teens because pediatricians are seeing increasing numbers of patients whose excess weight may affect birth control effectiveness, Ott said. For example, hormonal patches may be less effective in girls weighing more than 198 pounds, the policy says. Also, obese girls are more likely to gain weight with hormonal injections than with birth control pills.