For decades, age two has been one of the most important checkpoints in HIE research.
There's a good reason for that. It's called the Bayley Scales of Development, and it's the most commonly used assessment for clinical trials. By 18–24 months, clinicians can assess important areas of development, including motor, cognitive and language skills. Many foundational studies of therapeutic hypothermia used this age as a primary neurodevelopmental endpoint.
But there is an equally important limitation:
A two-year-old hasn't had the opportunity to show us everything their brain will eventually be asked to do.
That matters tremendously when we talk about HIE outcomes, as we know the research shows different impacts may emerge well into childhood.
Think about what we ask of a toddler compared with an eight-year-old.
An eight-year-old may need to:
Many of these abilities rely on higher-order cognitive skills that are still developing in toddlerhood, and are impossible currently to assess and predict. In fact, research shows the Bayley has significant limitations to predict neurocognitive deficits in school age.
Researchers now have some emerging data from following children with HIE well beyond toddlerhood, albeit in smaller cohorts currently.
The landmark NICHD Neonatal Research Network follow-up evaluated children from the original therapeutic hypothermia trial again at ages 6–7, examining not only survival and disability but also cognitive, attention, executive-function and visuospatial outcomes.
The TOBY trial also followed children to ages 6–7, demonstrating why school-age follow-up provides information that simply isn't available during infancy.
But one particularly important study looked at a group that can easily be overlooked: children who had been cooled for HIE but did not have cerebral palsy.
At ages 6–8, Lee-Kelland and colleagues found differences in cognitive, motor and behavioral outcomes compared with matched peers.
Children with a history of HIE had lower average scores in areas including full-scale IQ, perceptual reasoning, working memory, processing speed and motor performance.
They also experienced more emotional and behavioral difficulties.
And 34% required additional support in school compared with 5% of matched controls.
These were children who did not have one of the most visible major motor outcomes traditionally associated with HIE. The differences were more subtle, but subtle does not mean unimportant. Many children require help in school, behavioral interventions, parent coaching, and other accommodations and interventions.
Later-emerging HIE impacts can involve areas such as:
A review of cognitive outcomes in late childhood and adolescence emphasizes exactly this point: apparently normal development in early childhood does not necessarily exclude later cognitive and behavioral difficulties because many higher cognitive functions cannot be fully evaluated at younger ages.
Families sometimes hear this when concerns emerge later.
And it's important to understand: The earlier assessment may not have been wrong.
A child may genuinely have been doing very well at two. Their brain did not necessarily suddenly become injured at eight. Instead, the demands placed on the brain changed. As academic, organizational, behavioral and social demands increase, differences that weren't measurable earlier may become visible.
Long-term follow-up shouldn't mean spending childhood waiting for something to go wrong as many children with HIE continue to do very well.
The purpose of surveillance is the opposite:
If a need emerges, we want to recognize it early enough to help.
Recognition creates access to support.
Age two gives us valuable information, but it doesn't give us all the information. Being told at six months old that your child will be unaffected is wonderful news, but it may not be accurate. You and your child deserve honest information, and reassurance of their development.
Children's brains continue developing, and the demands placed upon them become much more complicated through childhood and adolescence.
That's why Hope for HIE continues to advocate for developmental surveillance that looks beyond early motor milestones and beyond the toddler years.
Learn more about the full spectrum of HIE outcomes and what research tells us from infancy through school age and beyond in our HIE Outcomes resource.
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