Amy Grossberg was ordered imprisoned for 2 1/2 years, and Brian Peterson, for 2 years.
Peterson, 20, remained steady during the sentencing hearing, unlike Grossberg, who sobbed while addressing the judge. Neither looked at the other in the courtroom.
Assistant Attorney General Paul Wallace argued that "Grossberg was responsible through action or inaction, and in doing so showed a chilling indifference to his life."
But psychiatrists who have studied neonaticide, say the mothers are not guilty of premeditated murder. They are instead mentally impaired.
"Mistakes were made that cost my son's life and all I can say is I'm so sorry for what happened," Peterson told Judge Henry duPont Ridgely.
Grossberg told the judge she was "extremely sorry" and blamed herself. She said "I love you" to her family as she was led out of the courtroom crying.
Both defendants, whose legal strategies pitted them against each other, could have been sentenced to 10 years in prison. Sentencing guidelines suggested 2 and 1/2 years. Both were credited for two months already served. Anthony Farina, a spokesman for the Delaware Department of Correction, said inmates in Delaware typically serve 90 percent of their sentences.
The judge sentenced Peterson to 8 years, with all but 2 years suspended. Grossberg was sentenced to 8 years, with all but 2 and 1/2 years suspended. Both will also be required to perform 300 hours of community service.
Both have spent most of their time since their November 1996 arrest at the homes of their parents in the wealthy northern New Jersey suburb of Wyckoff.
"I'm extremely sorry for what happened to my baby," Grossberg told the judge. "I blame nobody but myself. It's something I'll never be able to forget. That pain inside will be with me for the rest of my life."
Prosecutors said Peterson told them he and Grossberg had twice scheduled an abortion, but that she had backed out both times.
Prosecutor Peter Letang read letters Grossberg wrote to Peterson before the baby was born in secret on Nov. 12, 1996, at a Newark, Del., motel, in which she said she wanted her pregnancy to "go away."
"Why won't it just go away? Haven't we suffered enough?" Grossberg wrote. "What did we do to deserve this? All I want is for it to go away. I can't get caught."
Her attorney, Robert Tanenbaum, said Grossberg regularly visits her baby's grave and is consumed by depression.
The two former sweethearts from the New Jersey suburb of Wyckoff were both freshmen in college when they went to a Newark, Del., motel room Nov. 12, 1996, and delivered a baby boy after a hidden pregnancy. The newborn's body was later found in a plasic bag in the motel's trash bin.
The state medical examiner's office said the boy was born alive at full term and died of multiple skull fractures caused by blunt trauma and shaking.
Grossberg and Peterson were originally charged with first-degree murder, and prosecutors had threatened to seek the death penalty. After their arrest, the two teen lovers appeared united, holding hands in early court appearances. But later, their defense strategies set them against each other.
In March, Grossberg's lawyers indicated in court papers that she believed the child was stillborn and that, if any crime had been committed, it was by Peterson.
A short time later, Peterson pleaded guilty to manslaughter and promised to testify against his former girlfriend. He told prosecutors he believed the baby was stillborn and put it in a plastic bag in the trash after Grossberg yelled, "Get rid of it!"
Grossberg pleaded guilty to manslaughter a month later.
Peterson was a freshman at Gettysburg College in Pennsylvania at the time of the baby's death. Grossberg, also a freshman, was an art student at the University of Delaware.