It was the third attempt in recent years to grant "personhood" to the unborn.
Voters across most demographic groups rejected Amendment 67 in Tuesday's election, according to preliminary exit poll results. It was rejected by voters who identified as Democrats and Independent or other. Republicans were about split.
The measure also had significant opposition among those who opposed abortion and those who identified as evangelicals or born-again Christians.
The personhood issue was an important part of the U.S. Senate race, with Sen. Mark Udall highlighting congressman Cory Gardner's past support of measures to grant legal rights to fertilized eggs. Gardner voters were about split on the issue.