Researchers Gladys Martinez, Casey Copen and Joyce Abma at the National Center for Health Statistics at the Centers for Disease Control and Prevention said the probability of a teen birth before age 20 was the same in a similar study in 2002.
In 2006 to 2010, the probability of females ages 15-24 having given birth by age 15 was less than 1 percent, compared with 18 percent by age 20, the report said.
"Hispanic teenagers had the highest risk of having a teen birth. Non-Hispanic black teenagers' probability of having had a first birth between the ages of 15-19 was higher than that of non-Hispanic white teenagers but lower than for Hispanic teenagers," the report said.
Fourteen percent of non-Hispanic white females had a first birth by age 20, compared with 26 percent of non-Hispanic black and 30 percent of Hispanic females, the report said.
The U.S. birth rate for females ages 15-19 was 39.1 births per 1,000 females in 2009 -- a historic low -- but the rate was higher than in a number of other developed countries. The United Nations Population Division said the teen birth rate in Canada was 14 births per 1,000 female teens; in Germany, it was 10 births per 1,000 female teens; and in Italy, 7 per 1,000 female teens, the report said.