A coroner is to hold a full inquest on the death of baby Luke Winston-Jones, from Anglesey, who died last week.
Ruth Winston-Jones took Luke's case to the High Court
Coroner Andre Rebello said it was not normal to hold an inquest for a natural death, but said issues raised by Luke's family needed answers.
An inquest was opened in Liverpool on Tuesday and adjourned until 10 January.
Luke, who had terminal heart and breathing problems, was at the centre of a High Court case between Alder Hey hospital in Liverpool, and his family.
The two sides had disagreed about the care Luke would receive if his condition worsened.
Medical experts had been concerned about the effects of further "aggressive" treatment, but his mother Ruth Winston-Jones did not want any measures ruled out in advance.
The High Court ruled that doctors could withhold mechanical ventilation, but, in a last-minute concession, decided he could still have the chance to receive cardiac massage.
Shortly after Luke's death last Friday, his family demanded an inquiry into the care he was given at Alder Hey hospital in the hours before he died.
In response to the call, a spokesperson for the hospital said it could not respond to specific allegations, but "refutes allegations that Luke did not receive the best care and attention at Alder Hey."
Speaking at the opening of the inquest on Tuesday, Mr Rebello said four pathologists who had examined Luke had agreed that he died of natural causes.
"I understand that Luke died from a cardiac arrest because it was the end of his life," he said.
But he added that questions from the family meant he would be holding a full inquest.
"It would be difficult not to hold an inquest now," he said.
After the hearing, Ms Winston-Jones said she "did not want to make anyone's life difficult".
Luke's case was the focus of media attention
"I'm just fighting for my beautiful little boy," she said.
Luke, who had the rare Edwards Syndrome, died at Alder Hey - he had never left hospital.
Few babies who are born with the condition, which severely affects most organs of the body, survive beyond a year.
Luke was born by emergency Caesarean at Ysbyty Gwynedd in Bangor on 30 January.
Due to his serious cardiac defects, including two holes in the heart, he was then moved to Alder Hey.
Luke's case went to the High Court only two weeks after a judge ruled that another seriously ill baby, Charlotte Wyatt, should not be given aggressive treatment but should be allowed to die peacefully.
On Monday, Ms Ruth Winston-Jones said her son's funeral, which will take place on Saturday, would be open to the public.