Birthrate continues to decline in the U.S.

American women are delaying having children and having fewer of them, setting new record lows in birthrate data, the federal government said Friday.

In 2011, 3,953,590 births were registered in the United States, down 1 percent from the previous year.

This was the smallest number of U.S. births since 1998, and represented declines in the white, black and Hispanic populations, researcher Joyce A. Martin and colleagues at the National Center for Health Statistics say in their new report, “Births: Final Data for 2011.”

The nation’s general fertility rate fell again, to a historical low of 63.2 births per 1,000 women ages 15 to 44.

This overall contraction in childbearing was also seen in the nation’s total fertility rate, which dipped to 1.89 children per woman — well below the 2.1 children-per-woman replacement rate that a nation needs for demographic stability. The U.S. fertility rate was at replacement level in 2007, but it has been falling ever since, the researchers note.

As has been often reported, the birthrate for teens ages 15 to 19 has regularly fallen to a historic low, and 2011 was no different: The teen birthrate dropped 8 percent, to 31.3 births per teen, from 2010 to 2011.

The number of babies born to these teens also dropped to 329,772 — the fewest in 65 years, researchers said, referring to the 322,381 births to teens in 1946.

Moreover, birthrates to women in their early 20s fell to a record low in 2011, while the rate for women in their late 20s fell to a level not seen since 1976.

The birthrate for women in their early 30s was stable, but rose for women in their late 30s and early 40s.

Among women in their 50s, the number of births was slightly higher, with 571 births in 2010 and 585 births in 2011, the Center for Health Statistics said. The number of births to women in their 50s has been steadily increasing since 1997, when there were 144 births, they said, adding that “fertility-enhancing therapies” have played a role in increasing birthrates for all women 35 and older.

Another important data marker — the portion of births to unmarried women — remained stable in 2011, with 40.7 percent of births out of wedlock.

This is higher than in previous decades — in 1980, about 18 percent of births were to unwed mothers, while in 2000, it was 33 percent.

When unwed births were examined by race or ethnicity, 72 percent of black births were unwed, as were 66 percent of Native American births, 53 percent of Hispanic births, 29 percent of white births, and 17 percent of Asian/Pacific Islander births.

These proportions were “essentially unchanged” from the previous year, Ms. Martin and her colleagues said.