DENVER (KDVR) — Coloradan women are becoming less and less interested in having children.

Women in the U.S. and much of the developed world have been experiencing a drop in fertility rates in the 21st century. In Colorado, the trend has been especially pronounced. It has one of the nation’s lowest fertility rates and saw one of the sharpest declines in birth rates over the last 15 years.

The fertility rate differs from the birth rate. While the birth rate measures the number of children born for every thousand people, the fertility rate measures how many children are likely to be born per woman in childbearing years.

Demographers estimate fertility rates need to be around 2.1 in order for a country to continue growing in population. Like much of the developed world, U.S. fertility rates are below replacement level.

At 1.48, Colorado’s fertility rate was the sixth-lowest in the U.S. in 2020, the most recent year tracked by national vital statistics.

Colorado’s total fertility rate is 1.48, lower than the national rate of 1.64 and well below the replacement level. Only Maine, Massachusetts, New Hampshire, Oregon, Rhode Island and Vermont have lower fertility rates.

Low fertility rates broadly track with high income and education levels. The states with the lowest rates are concentrated along the West Coast, New England and the Southwest.

Not one state has a replacement-level fertility rate. Even the highest – the Dakotas, Nebraska, Utah and Alaska – come short of 2 children per woman.

This trend has been years in the making. Every state in the U.S. has a lower fertility rate now than 10 years ago. Colorado had one of the sharpest downswings.

Colorado’s fertility rate plummeted by 23% from 2010 to 2020. Only Arizona had a bigger drop in fertility.

Surrounding states have seen the same trend develop, some U.S. regions have seen fertility drop much faster than others. Western states – those that touch the Rocky Mountains and further west – have seen fertility rates decline by almost twice as much as the rest of the U.S.