Jurors will choose among first-degree murder, second-degree murder and manslaughter if they find Lindsay Clancy guilty of the strangling deaths of her three children during deliberations that are expected to begin on Thursday.

The option of a manslaughter verdict, which Judge William Sullivan of Plymouth County Superior Court said on Wednesday that he would allow, could potentially help jurors reach consensus sooner and make the prospect of a hung jury less likely.

“It’s certainly a positive development,” said Kevin Reddington, Ms. Clancy’s chief defense lawyer.

Ms. Clancy, 36, does not deny strangling her children — Cora, 5, Dawson, 3, and Callan, 8 months. But she has pleaded not guilty, saying she should not be held criminally responsible for the killings because she was suffering from postpartum psychosis when she strangled them with exercise bands on Jan. 24, 2023.

She faces life in prison without parole if she is convicted of first-degree murder. If acquitted, she would most likely be committed to a secure psychiatric institution for an indefinite period.

Witness testimony concluded on Wednesday in the trial that started last month in Plymouth, Mass., with testimony from Gregory Saathoff, a forensic psychiatrist who is an expert witness for the prosecution. On Thursday, lawyers on each side will have an hour to present closing arguments before the case goes to the jury, Judge Sullivan said.

After dismissing the jury for the day, Judge Sullivan considered arguments from the lawyers about how to instruct jurors ahead of their deliberations.

Ken White, a criminal defense lawyer based in Los Angeles, said that asking for a manslaughter instruction is a fairly typical defense strategy, “to give the jury a middle ground.”

“Juries bargain all the time,” Mr. White said, adding, “That’s not what they’re supposed to do. But they do it.”

Mr. Reddington argued unsuccessfully for an instruction telling jurors that if they saw evidence of a flawed police investigation, it could be a reason to acquit Ms. Clancy.

Investigators, he said, “basically accepted the fact that she strangled the kids, the kids were in the basement, she’s guilty, and we can move on. They didn’t investigate anything.”

Shanan Buckingham, a prosecutor, disputed his claim. She said the evidence showed that there had been an adequate police investigation.

Though Judge Sullivan didn’t agree to include the instruction, he said that Mr. Reddington can still raise the proposal in his closing argument on Thursday. He said he would provide the written jury instructions to lawyers on Thursday morning.

Expert witnesses for Ms. Clancy’s defense have said she was suffering from postpartum psychosis, a condition that can cause hallucinations and delusions, when she strangled her children at their home in Duxbury, Mass. Multiple witnesses testified that Ms. Clancy had reported hearing a voice commanding her to kill her children and herself.

Dr. Saathoff and other prosecution experts have said that based on their assessment of Ms. Clancy’s mental state at the time, the killings were not necessarily the result of psychosis and were more likely an attempt to take her children with her when she tried to commit suicide.

The trial, which has divided Americans, has drawn significant attention, with spectators crowding the courtroom and hundreds of thousands of people watching livestreams of the hearings.

After closing arguments on Thursday, 12 of the 18 jurors who were seated for the trial will be randomly selected to deliberate, with six others designated as alternates. The pool of 18 includes 12 women.

“Go home, rest up, and be ready for tomorrow,” Judge Sullivan told jurors as he dismissed them for the day.

If you are having thoughts of suicide, call or text 988 to reach the 988 Suicide and Crisis Lifeline or go to SpeakingOfSuicide.com/resources for a list of additional resources.