The mother, Michelle Wilkins, answered a Craigslist ad for baby clothes on March 18.
When she arrived at the purported seller's home in Longmont, she was attacked, beaten, cut open and her fetus was removed. The baby did not survive.
Wilkins was treated at a hospital and later released
The alleged attacker, Dynel Lane, 34, is being held on a $2 million bond.
After the attack, prosecutors said it may be hard to muster a murder charge. Colorado state law does not recognize a fetus as a person, unless it is capable of surviving for a period of time outside the womb, a prosecutor said then.
But the extent of the period that the fetus must survive in order to be defined as a baby is not legally clear.
Lane's husband, David Ridley, told police he found the baby on the day of the attack in a bathtub taking a breath.
While the attack on Wilkins has shocked her community for its brutality, many have also remarked on the 26-year-old's strength.
Bleeding and stunned in a stranger's basement, Wilkins managed to lock herself in a room to prevent any further violence, called 911 and did what she could to stem the bleeding.
Police officer Billy Sawyer, who responded to the call, said he and his partner weren't prepared for the grisly scene.
"She was covered in blood," Sawyer told CNN's Erin Burnett. Wilkins reached out for his hands for comfort. He held them and listened to her. "She did not know she was no longer with her child," he said.
Her strength and willpower had impressed him
, as she directed him by phone to her location while she bled so heavily. "She is the only reason why she's alive right now," Sawyer said.
Wilkins' family started a GoFundMe page to raise money for her care. A note on the page said that she's "in a safe location" and "surrounded by family and friends."
More than $73,000 of the $75,000 goal have been raised so far.