Birth rates in the United States have reached 30-year lows, according to data from the U.S. government.

Research from the Centers for Disease Control and Prevention shows that birth rates declined for all groups: teens, women in their 20s and 30s.

In total, there were 3.853 million births last year, the lowest since 1987. The total for 2017 was 92,000, less than 2016.

Researchers say several factors could be driving the drop. One possible cause could be that millennials, who are in their prime childbearing years, are choosing to have fewer children later in life, if they choose to have children at all.

Another factor may be changing immigration patterns. Asians, who increasingly are a larger share of net immigration to the U.S., tend to have fewer children than other immigrant groups.

According to LiveScience, a science news website, one reason may be the lingering economic unease many Americans are still feeling in the aftermath of the Great Recession.

“People feel just really uncertain about the future,” Karen Benjamin Guzzo, associate director of the Center for Family & Demographic Research at Bowling Green State University in Ohio, told Live Science. “And that generally does not bode well for having kids.”

According to The Associated Press, the CDC found:

The rate of births to women ages 15 to 44, known as the general fertility rate, sank to a record low of about 60 per 1,000

Women in their early 40s were the only group with higher birth rates in 2017, up 2 percent from the year. The rate has been rising since the early 1980s

The cesarean section rate rose by a tiny amount after having decreased four years. Studies have shown C-sections are more common in first-time births involving older moms

Rates of preterm and low birth weight babies rose for the third straight year, possibly for the same reason

Birth rates for teens  continued to nosedive, as they have since the early 1990s. In 2017, they dropped 7 percent from the year before

Rates for women in their 20s continued to hit record lows. They fell 4 percent

Perhaps most surprising, birth rates for women in their 30s fell slightly, dipping 2 percent for women ages 30 to 34, and 1 percent for women 35 to 39.