WASHINGTON — The fertility rate in the United States fell in 2018 for the fourth straight year, extending a steep decline in births that began in 2008 with the Great Recession, the federal government said on Wednesday.

There were 59.1 births for every 1,000 women of childbearing age in the country last year, a record low, according to the National Center for Health Statistics. The rate was down by 2 percent from the previous year, and has fallen by about 15 percent since 2007.

In all, there were 3,791,712 births in the country last year, the center said in its release of final birth data for 2018.

Fertility rates are essential measures of a society’s demographic balance. If they are very high, resources like housing and education can be strained by a flood of children, as happened in the postwar Baby Boom years. If they are too low, a country may find itself with too few young people to replace its work force and support its elderly, as in Russia and Japan today.