essarily support one. Despite a minor increase in 2006, the rate of pregnancies among teen girls has been on a downward trend since 1991. Another indicator, the incidence of sexually transmitted diseases, is alarmingly high: nearly 1 in 4 girls ages 14 to 19 and nearly 1 in 2 African-American girls, according to the Centers for Disease Control and Prevention. But this is the first year such a study has been completed, and the study doesn't separate 14-to-16-year-olds from 17-to-19-year-olds, so it's still unclear which way that trend is heading.