WASHINGTON -- Almost one-fifth of teenage mothers in the United States give birth to a second child before age 20, limiting their chances of finishing their educations or landing jobs, a government report said.While teen birthrates have been falling in the U.S. for two decades, more than 367,000 girls ages 15 to 19 had children in 2010, the Centers for Disease Control and Prevention said in a report Tuesday. About 18 percent of those were repeat births, the Atlanta-based agency said.The analysis found that the repeat births are most common in a band of southern and western states -- Texas, Arkansas, Louisiana, Mississippi, Georgia, Oklahoma, Nevada and Arizona."When young mothers postpone a second birth, they have greater educational and job opportunities," Leslie Kantor, vice president of education at Planned Parenthood Federation of America, said in a statement. "The best way to prevent teen pregnancy across the board is by investing in effective sex education, encouraging teens to talk to their parents, and ensuring access to birth control."Only 20 percent of teenage mothers use the most effective birth control available, including hormonal implants and intrauterine devices or IUDs that don't require daily maintenance, the CDC said. Even so, births among teenagers are waning. The agency said 19.5 percent of teenage births in 2007 were second or later children.The Affordable Care Act, may help reduce teen births because it requires insurers to cover contraceptives without out-of-pocket charges to patients, Kantor said. In five of the states with the highest rates of repeat teen births -- Texas, Oklahoma, Louisiana, Mississippi and Georgia -- Republican governors have resisted the law, refusing to build new insurance marketplaces or expand Medicaid.