Judge Gary Fenner handed down the sentence after a jury recommended the death penalty for Lisa Montgomery in the slaying of Bobbie Jo Stinnett.
The 39-year-old was convicted in October of kidnapping resulting in death in the Dec. 16, 2004, killing of Stinnett. Montgomery was arrested at her farmhouse a day after showing off Stinnett's baby as her own.
In October, jurors deliberated more than five hours before recommending the sentence for Montgomery.
Showing jurors photos of the bloody crime scene, theMontgomery deserves to die because of the heinousness of her crime, and because computer evidence - including Internet searches on performing Caesareans - shows the crime was premeditated.
During the trial, defense attorneys claimed Montgomery was suffering from pseudocyesis, which causes a woman to falsely believe she is pregnant and exhibit outward signs of pregnancy.
They portrayed her as a victim of severe mental illness whose delusion of being pregnant was being threatened, causing her to enter a dreamlike state when the killing took place.
They also argued that she had post-traumatic stress disorder brought on by mental, physical and sexual abuse in her childhood.
The federal prosecutor in the case, Roseann Ketchmark, called the pseudocyesis claim "voodoo science."
She said Montgomery was driven by fear because she believed her ex-husband, Carl Boman, would expose that she was lying about being pregnant and use it against her as he sought custody of two of the couple's four children. A custody hearing had been set for January 2005.
Montgomery becomes the third woman on death row in the federal prison system.