Editor's Note: This story includes discussion of suicide. If you or someone you know needs help, the national suicide and crisis lifeline in the U.S. is available by calling or texting 988.

Jury selection began Monday in the trial of a Massachusetts mother who strangled her three children while undergoing medical treatment for psychiatric problems that developed after she gave birth.

The trial of Lindsay Clancy, a former labor and delivery nurse at Massachusetts General Hospital, could take several weeks and is expected to explore the complicated and rare phenomenon of postpartum psychosis, which afflicts a very small percentage of women who develop delusions and sometimes hallucinations after childbirth.

Five jurors were selected Monday. A total of 18 jurors, including six alternates, will be chosen for the trial.

Clancy's lawyers -- and her husband -- say she was not responsible for her actions. Defense attorney Kevin Reddington doesn't dispute that she killed the children, but plans to raise an insanity defense.