A government report from the Centers for Disease Control and Prevention shows teen pregnancies fell again last year, to another historic low. Last year, the birth rate for US teens dropped 8-percent. Rates have been falling since 1991. Experts cite a range of factors, including less sex, positive peer influence, and more consistent use of birth control. The new report is based on a review of most of the birth certificates filed last year. There were nearly 4 million births. That's down slightly from the 2014 total, by about 4,300. The C-D-C released the data as part of a report on US births in 2015.