DENVER (KDVR) — Colorado’s expenses, labor economics, education levels and culture all play a role in low fertility.

It looks like a statewide low sex drive might have something to do with it, too.

Colorado’s birth rate has been sliding and is one of the lowest rates in the U.S. now. Despite being among the states where women are most likely to be married, Colorado’s women are also some of the least likely in the nation to be mothers.

Studies show several possible reasons. There is a link between women’s education and professional success and their likelihood of childbearing, and Colorado’s women are among the most educated and the highest earning. Further, Colorado cities are some of the most expensive in which to raise children, and Colorado is among the most expensive states in which to give birth at all.

Coloradans have less sex, too, according to a survey from NapLab, a sleep equipment research firm. The survey quizzed 1,600 people on their frequency of sex, and none reported less than Coloradans. Colorado’s respondents reported having sex an average of 0.42 times a week – less than half the national average and the lowest frequency in the U.S.

Alaskans, on the other hand, reported having sex 2.8 times per week, the nation’s highest. New Mexico had the next highest with 2.064 times per week, then Vermont, Arkansas and Indiana.

At the bottom of the list are Colorado, Maine, Michigan, Nebraska and West Virginia.