Strict rules about the administration of morphine were not followed at Stafford Hospital, contributing to the deaths of twin brothers Harry and Alfie McQuillan, a hearing was told.
It is said the babies were given more than 10 times the proper dose of the drug after being delivered by emergency Caesarean section at just 27 weeks.
Both babies were transferred to University Hospital of North Staffordshire in Stoke-on-Trent afterwards but it was too late and the twins died two days later.
The episode unfolded hours after their birth on October 30, 2010, in Stafford’s Special Care Baby Unit, where Joanne Thompson was the senior nurse in charge of the night shift.
Following the births, a consultant paediatrician told the team to administer morphine to the boys and prescribed a set amount of the drug.
Strict hospital rules required two nurses to be present when medication was drawn up, but Thompson delegated the task to another nurse and a junior doctor, the NMC hearing was told.
Neonatal nurse Hayley Amos came on duty in the unit shortly after the morphine was administered to both babies at around 7am.
She said: “It became apparent that whoever had checked and set up the infusion had somehow miscalculated, and had set the pumps to deliver a much higher volume of morphine solution.”
Both pumps were immediately turned off, the panel heard.
“Joanne went very quiet at this point, and was visibly shocked,” said Ms Amos.
She said the other nurse, Lisa Lucas, was “hysterical” and kept saying “Oh my God, what if I’ve killed these babies?” while crying and shaking.
Both nurses were suspended the same morning, but Thompson returned to work just days later on November 2, before a disciplinary inquiry got underway.
After being told of her suspension, Thompson told Ms Amos: “I can’t believe this – I didn’t have anything to do with the morphine.”
An inquest into their deaths resulted in a narrative verdict, with the coroner saying the twins died of complications of prematurity but that the excessive dose of morphine was a likely factor for their deaths and that there had been failings in their care.
Stafford Hospital has apologised to the parents.
Following the inquest last year, the boys’ mother Ami Dean, from Stafford, said: “I could have coped with them dying from prematurity, as that would have been nobody’s fault.”
Thompson admits not being present throughout when the morphine was administered to both twins, or checking that the dosage was correct, and not summoning help to check the drug.
She denies the remaining charges against her.
If found guilty of misconduct she could be kicked out of the profession.
The hearing continues.