The number of women in the United States who gave birth dropped last year, according to federal statistics released Thursday, extending the decline for a sixth year.

The National Center for Health Statistics reported Thursday that there were 3.93 million births in the United States in 2013, down slightly from 3.95 million in 2012, but 9 percent below the high in 2007.

According to the report, the general fertility rate in the United States — the average number of babies women from 15 to 44 bear over their lifetime — dropped to a record low last year, to 1.86 babies, well below the 2.1 needed for a stable population. For every 1,000 women ages 15 to 44, there were 62.5 births in 2013, compared with 63 the previous year.

The decline is especially notable because the number of women in their prime childbearing years, 20 to 39, has been growing since 2007.