Warning: This story contains distressing details and discussion of attempted suicide

The fate of US mother Lindsay Clancy is now in the hands of a Massachusetts jury, who must decide if she is guilty of first-degree murder – the intentional and premeditated killing of another person – in the deaths of her three children.

For five weeks, the trial has gripped the country as Clancy’s lawyers have argued that she was suffering from postpartum psychosis when she killed her children, who ranged in age from eight months to five years. Clancy does not deny killing her two sons and daughter.

The prosecution argued she made a calculated decision to intentionally murder them.

The jury could find Clancy guilty of first-degree murder, guilty of lesser charges, or not guilty.

The jury of nine women and three men completed their first day of deliberations on Thursday. They will return on Friday.

In the state of Massachusetts, a first-degree murder conviction carries a mandatory life in prison sentence without the possibility of parole.

The jury could instead find Clancy guilty of second-degree murder – committed with malice or extreme recklessness, but without prior planning – or involuntary manslaughter – causing death because of extreme carelessness. Those convictions, too, would lead to some prison time.

If Clancy is found not guilty by reason of insanity, then she will not be set free, but instead sent to a psychiatric hospital, where she possibly could remain for life.

Attorneys for both sides made closing arguments on Thursday before the jury began deliberating.

Kevin Reddington, Clancy’s lawyer, repeated the defence’s argument that she was experiencing postpartum psychosis when she killed the children with exercise bands at their home and then attempted to end her own life by jumping out of a window. Clancy was paralysed by the attempt and has attended the trial in a wheelchair.

“This young lady is not guilty of the killing of her children because she was suffering from a disease and defect,” Reddington said, adding that he believed prosecutors were “not going to be able to prove otherwise”.

The UK’s National Health Service (NHS) defines postpartum psychosis as a rare and serious mental health illness that can affect someone soon after having a baby, and which should be treated as a medical emergency.

One of the more tense moments of the closing arguments came when Reddington directly addressed the prosecutors and asked them to explain why they tried to prove Clancy’s suicide attempt was not serious. The judge interrupted and ordered him to address only the jury.

Prosecutor Jennifer Sprague did not dispute that Clancy was mentally ill, but told the jury that the defendant could tell the difference between right and wrong at the time of the killings.

“It’s not the system or the DSM that caused her to strangle her kids,” Sprague told the jury, referencing the US encyclopaedia of mental heath diagnoses, which does not give postpartum psychosis its own classification.

Sprague also said Clancy had an “abundance of care”, but had hidden thoughts from doctors about harming her kids.

If you are suffering distress or despair and need support, you could speak to a health professional, or an organisation that offers support. Details of help available in many countries can be found at Befrienders Worldwide. www.befrienders.org.

In the UK a list of organisations that can help is available at bbc.co.uk/actionline.