The US fertility rate fell for a fourth year in a row in 2018 to the lowest level in about three decades. The 3,791,712 births—59.1 for every 1,000 women of childbearing age—was down 2% from 2017 and 15% from 2007, according to data out Wednesday. The total fertility rate—an estimate of the number of births a group of 1,000 women might have over their lives—also fell 2% to 1,729.5 births, per CNN. NBC News reports that's shy of the 2,100 births needed for the population to remain stable. Births began to fall with the economic downturn in 2008. But despite a small but brief increase in 2014, they've continued to decline even as the economy has recovered. Per the New York Times, demographers are trying to figure out if this is "a temporary phenomenon or a new normal, driven by deeper social change."
A decline was seen across nearly all age groups, with the greatest drop in births among teens. They fell 7.4% from a year before. Only women in their late 30s and early 40s saw increases in birth rates, which may be driving a slight increase in births delivered at less than full term, per CNN. Data showing more than half of women who had children in their late 30s had college degrees, compared to a smaller percentage of women who had children in their late 20s, "suggest that people want to establish themselves before having children … to make sure they have adequate resources," Alison Gemmill, a demographer at Johns Hopkins University, tells the Times. She says childlessness is not a concern as the typical woman will have two children by her mid-40s. Immigration to the US has so far offset declines in fertility. (Read more birth stories.)