BELFAST – Jurors heard conflicting medical testimony Tuesday about the mental state of a young Searsport mother the day she smothered the life from her infant son.

While psychiatrists representing Natachia Ramsey described her as suffering from a severe form of depression brought on by her son’s birth four weeks earlier, a physician testifying for the state discounted the role of mental illness in the case.

Ramsey, 26, is being tried in Waldo County Superior Court to determine whether she should be held criminally responsible for the April 11, 1999, death of her son, Hunter Macarthy Ramsey, at a Searsport home. Ramsey has pleaded guilty to manslaughter against her son but has also pleaded not guilty because of mental defect or disease.

The trial opened Monday, and the defense rested shortly before noon Tuesday after calling three witnesses. Ramsey testified in her own behalf. The other two witnesses were medical professionals who focused on her mental state leading up to the day of the child’s death. Both witnesses centered on postpartum depression, an imbalance that causes despondence in mothers after giving birth, as the reason Ramsey killed her baby, then slashed her wrists in an attempt to take her own life.

Dr. Muriel Sugarman, a psychiatrist at the Augusta Mental Health Institute, held scores of clinical sessions with Ramsey during her five-month incarceration. Ramsey has been living in a supervised group home in Rockland since her release from AMHI.

Sugarman, who described herself as an expert in postpartum depression, intimated that Ramsey was a textbook case. She said the woman’s volatile, unstable upbringing was typical of mothers who harm their children and themselves. She said depression ran in Ramsey’s family, as evidenced by the suicides of her mother and her grandfather while she was in her early teens.

Sugarman told the jury that Ramsey had been frazzled and disoriented by the recent collapse of her marriage and the arrival of the baby, that she reached a point where she believed suicide was the only way out. Before she could do that, however, she would need to dispose of her month-old baby.

“Her understanding of reality was very distorted,” Sugarman testified Tuesday. Sugarman said Ramsey believed “she had to die and she could not leave the baby alone because no one would take care of the baby if she was dead. … She saw no way out. She saw no way to solve her problems. … I think her brain just was not working right.”

Assistant Attorney General Fernand LaRochelle pressed Sugarman on the extent of Ramsey’s depression.

Ramsey’s ability to reason her way out of the situation allegedly was overpowered not by a psychotic episode but by biological and chemical changes that took place during pregnancy. When LaRochelle asked whether Ramsey fit the definition of a psychotic, Sugarman replied, “I don’t believe so.”

Sugarman acknowledged there was no medical record of Ramsey’s experiencing postpartum depression after the birth of her daughter six years earlier.

That absence of an earlier postpartum episode was raised again when LaRochelle called his expert witness, Dr. Neil MacLean, a forensic psychologist contracted by the state to examine Ramsey.

MacLean testified that women usually experience postpartum depression after the birth of their first child, and less frequently after subsequent births.

While MacLean acknowledged that he had only two face-to-face sessions with Ramsey, he testified the he was able to make a diagnosis based on clinical records compiled by AMHI and the Waldo County General Hospital.

MacLean said that while Ramsey suffered from “severe major depression at about the time of the episode,” he concluded that she was competent to stand trial and could distinguish right from wrong. MacLean said that while Ramsey carried personality traits that left her susceptible to major depression and that could lead her to make bad judgments, they would not cause her to lose touch with reality.

“Depression triggers bad judgment, not a loss of contact with reality,” he said. “There’s a vast difference between bad judgment and breaking contact” with reality.

MacLean said there was no clinical evidence of Ramsey’s ever experiencing hallucinations or delusions: “If they’re not there, you’re not psychotic.”

At the conclusion of MacLean’s testimony, Justice Donald H. Marden recessed the trial until this afternoon.