Fewer unmarried women in the United States are having children, according to federal health officials.

According to a report from the U.S. Centers for disease Control and Prevention, births outside of marriage accounted for 40.6 of all births in 2013, 7 percent lower than the peak in 2008. The notable exception was with those who are older than 35 years, HealthDay reported.

In 2013, there were 1.6 million births to unmarried women younger than 35 -- the lowest since 2005, when there were 1.5 million births. The largest decreases were among teenagers and black and Hispanic women, according to the report.

"It's still high compared with previous generations, but there has been a decline," Sally Curtin, a statistician at the CDC's National Center for Health Statistics, told HealthDay.

Since the 1940s, there has been an increase in non-marital child-bearing; that climb represented a cultural shift, Curtin said.

The drop in births to unwed mothers since the 2000s reflects the decline in all births in the United States. The pattern began with the start of the recession in 2007.

"The fertility rate has declined, but the percent of decline in births to unmarried women has been greater," Curtin explained. "The areas that had the worst economic downturn also had the largest drops in the fertility rate."

However, the same report shows that more single women over the age of 35 are having children, even as "the overall birth rates for unmarried women in the United States have dropped," Reuters reported.

Unmarried women bearing children between the ages of 40 and 44increased 29 percent from 2007 to 2012 and 7 percent during that time for those aged 35 to 39.

"Many women are postponing births until their 30s, and the stigma of having a child outside of marriage has faded," Andrew Cherlin, a sociology professor at Johns Hopkins University who has studied the issue, told Reuters. He was not involved with the CDC report.

The federal health agency reported that birth rates for married women also dropped, but not as rapidly.