The research actually pools the results of nine studies looking at what life is like for the youngest surviving preemies when they reach four to eight years of age. The children in the studies were born between 22 and 25 weeks of gestational age, considered at this point to be the limit of viability. Few infants survive if they are born before 22 weeks.
The work was published Monday in the journal JAMA Pediatrics.
Lead author Dr. Gregory Moore of the Children's Hospital of Eastern Ontario (CHEO) said he and his colleagues did the study to have better information to give parents who want to know what their child might experience.
"Our purpose was to bring together the best quality cohort data to be able to have the numbers to start that discussion about: Are these babies having a good enough chance? Should they survive? And how can you start to discuss with parents around this very delicate topic?" said Moore, a neonatologist at CHEO and at the Ottawa Hospital.
"And our information, we hope ... will provide a framework around which to start to be able to speak with parents about whether or not to proceed with intensive care ... versus proceeding with palliative care ... and to assist the parents and the baby in a peaceful and comfortable way to allow the baby to pass away."
Dr. Steven Miller, head of neurology at Toronto's Hospital for Sick Children, called the work "an important contribution to our knowledge" about rates of neurodevelopmental issues facing the smallest of preemies.
Miller said he's often asked to counsel parents of premature infants about what to expect down the road. The data in this study will provide a good start point, he suggested — though he noted that while there are significant rates of neurodevelopmental impairments, there is also a glass-half-full side to the story.
"The rates here are substantial and I wouldn't want to minimize that. At the same time, there are babies doing well when they leave the neo-natal intensive care unit," Miller said Monday.
"At least half the babies are growing up without these impairments. And so it becomes important as well to look at the data from that perspective."
Miller said he sees that in his research.
"There is obviously a large group of babies that are born very young who do beautifully, and don't have moderate to severe impairments," said Miller.
"And so when you look at the 24- and 25-weekers, the question we're now asking more often is: how do we predict who's going to do well? And if parents knew that their babies were going to do well, would that help them care for their families during a very stressful intensive care stay?"
Miller said a study he and colleagues published a few years ago suggests that the illnesses a preemie develops after birth — infections or strokes or whatever — are actually key to establishing how well a premature child will do neurodevelopmentally later in life.
The CHEO study found results vary depending on the gestational week of the child's birth, with rates of impairment declining with additional weeks in the womb.
At 22 weeks, 43 per cent of children had moderate to severe impairment and 31 per cent had severe impairment. But the number of surviving children in this gestational group was small — only 12 combined in the studies.
As a result of the small number, those results have what is known as wide confidence intervals — the 43 per cent figure could be as low as 20 per cent or as high as 70 per cent. The corresponding confidence intervals for the rate of severe impairment at 22 weeks was also broad, ranging from 12 per cent to 61 per cent.
There were more survivors in the 23-, 24- and 25-week groups, which means the range of results in those groups was smaller. At 23 weeks, the rate of moderate to severe impairment was 40 per cent and the rate of severe impairment was 17 per cent.
At 24 weeks, 28 per cent of infants had moderate to severe impairment and 21 per cent had severe impairment. At 25 weeks, the rates were 24 and 14 per cent respectively.
Moore said a child with a severe impairment could have a profoundly low IQ or no useful vision. The child might have no ability to move without assistance or no capacity to hear. Such a child would not be expected to be able to live independently, he said.
Moderate to severe impairments are lesser variations of those conditions — higher IQs, some vision, some ability to hear with hearing aids, some ability to move about, perhaps with a walker or leg braces. These children would be able to make their way through school at least for a time, but would not likely go on to post-secondary education, he said. Some might be able to live independently.
Moore acknowledged having these types of discussions — putting a child's odds into numbers — is "very difficult."
"But some parents really do want to hear them and we need to be able to provide as accurate truth as we can about the potential outcomes and support parents in decision making at this really difficult time," he said.
"They're afraid. There's anxiousness. And we are doing our best to support them in every way that we can and to provide them with accurate information that they want to hear — if they want to hear it."