Desperately ill small babies in need of organ donations have "the odds stacked against them" because of current UK guidelines, experts have warned.
A "significant" number of newborn babies who die in intensive care in the UK could have donated organs to save another child's life if guidance permitted, researchers said.
Current protocols are at odds with those in place in other developed countries, said the researchers from Great Ormond Street Hospital (Gosh).
Their study, which took place at the renowned children's hospital's neonatal and paediatric intensive care units between 2006 and 2012, concluded that just over half of youngsters who died could potentially have been organ donors.
Of the 84 infants aged between 37 weeks and two months old who died, 45 (54%) could have donated organs if their parents had consented, they found.
The study, published in the Archives of Disease in Childhood, concludes that the potential for organ donation among young babies is "untapped" because of the guidelines around the way doctors define and diagnose death.
The guidance, created by the Academy of Medical Royal Colleges, "restricts" British doctors from diagnosing brain stem death in children who die before they are two months old, they said.
A diagnosis of brain stem death is the most common scenario for successful organ donation, they said.
They said the restriction is in contrast to the rest of Europe, the United States and Australia, where medics are able to diagnose death in younger babies using brain criteria.
Because of this limitation, a UK baby in need of a life saving heart donation - where only small newborn hearts are suitable for transplant - needs to wait until a donation is flown in from somewhere else in Europe.
The researchers said that if the guideline changed, more British babies would be able to donate hearts as well as their livers, lungs, kidneys and bowels.
At present youngsters can donate organs if the death was diagnosed by " circularitycriteria ".
But there are only around 60 paediatric organ donors annually in the UK, and there could be significantly more if the guidance was changed, the authors said.
"This research provides us with a glimpse of what might be possible in the UK if our guidelines around diagnosis of death in very young babies were brought into line with other countries," said Dr Joe Brierley, organ donation lead at Gosh.
"At Great Ormond Street we witness first-hand the urgent need for organs for children of all ages - but small babies particularly have the odds stacked against them because they need to be matched with the tiny organs of similarly-aged children.
"Organ donation is a very emotive topic, particularly when it involves children, but I believe it is an option that should be available to a young child's family if they decide it is the right choice for them.
"The loss of a child will always be an extremely tragic and heartbreaking experience, but a lot of parents who decide to donate their child's organs later find some comfort in the knowledge that at this most tragic time for their own family, they were able to do something extraordinarily kind to help another child - or perhaps several children."
A UK Donation Ethics Committee (UKDEC) spokeswoman said: " The UKDEC welcomes this study, and supports the need to offer donation to bereaved parents whenever possible.
"The existing guidance in relation to the diagnosis of brain-stem death in infants between 37 weeks gestation and two months of age is currently being reviewed by a working group of the Royal College of Paediatrics and Child Health which UKDEC is represented on.
"We would hope that any new guidance gives clarity to doctors caring for dying babies in the diagnosis of brain death and the opportunity to consider organ donation with the parents."