The birthrate for American teens hit an all-time low in 2013, and government statisticians attribute the decline to a reduction in teenage sexual activity and more widespread use of birth control among those who are having sex.

Preliminary birth certificate data collected by the Centers for Disease Control and Prevention shows that 277,749 babies were born in 2013 to mothers who were under the age of 20. That is the lowest figure for any year going back to 1940, according to a report released Wednesday by researchers in the CDC’s Division of Vital Statistics.

In 1940, there were 304,004 births to American teens, the report says.

The teen birthrate hit new lows for all age groups. There were 47.3 births for every 1,000 women ages 18 and 19; 12.3 births per 1,000 teen girls between the ages of 15 and 17; and 0.3 births per 1,000 girls ages 10 to 14. Among the 15- to 19-year-olds who accounted for nearly all teen births, the preliminary birthrate of 26.6 per 1,000 was 9.5 percent lower than it was in 2012.

All 50 states plus the District of Columbia recorded statistically significant declines in the teen birthrate between the years 1991 and 2012, according to the report. The size of these drops ranged from 24 percent in West Virginia and 25 percent in North Dakota to 64 percent in California and 65 percent in D.C. Overall, it was 52 percent.

Even when looking at the shorter period of 2007 through 2012, significant declines were recorded in D.C. and every state except West Virginia and North Dakota. These ranged from 19 percent in Oklahoma and South Dakota to 37 percent in Georgia and 39 percent in Colorado. Overall, the teen birthrate fell by 29 percent during those years.

CDC statisticians also noted that teen births dropped among young women of all racial and ethnic groups. Between 1991 and 2012, the steepest declines were seen for Asian-Americans (down 64 percent) and African-Americans (down 83 percent). For the most recent period between 2007 and 2012, the biggest drop was among Latina teens (down 39 percent).

In 2012, the most recent year with data sorted by race and ethnicity, the teen birthrates were 9.7 per 1,000 Asian-Americans; 20.5 per 1,000 whites; 34.9 per 1,000 Native Americans and Alaskan Natives; and 46.3 per 1,000 Latinas.

The result of all of these declines is that the overall teen birthrate has plunged 72 percent since its all-time high in 1957, when there were 96.3 births per 1,000 teen girls and women. (The total number of teen births peaked in 1970, at 644,708.)

One thing that has been on the rise is the proportion of teen births to unmarried mothers. Only about 2 percent of American teens were married in 2013; as a result, 89 percent of teen births that year were to single mothers. That’s up from 48 percent in 1980, 15 percent in 1960 and 14 percent in 1940, according to the report.

The historically low teen birthrate appears to be a sign that efforts to prevent teen pregnancies are paying off. A 23 percent jump in the teen birthrate between 1986 and 1991 prompted a flurry of public and private initiatives to promote abstinence and the use of birth control, and they’re working, the CDC researchers wrote.