Heart Surgery Saved Them. Now Researchers Are Following the Brain.

What four recent studies reveal about when developmental risk begins in babies born with heart defects — and what families can do about it

About one in every hundred babies is born with a heart defect. Surgery now saves the great majority of them, and attention has shifted to a quieter question: many of these children later find learning, talking, or moving harder than their classmates do. Four studies published in 2025 and 2026 trace where that risk begins — and, encouragingly, where some of it might be reduced.

Why doctors started paying attention to the brain and not just the heart

For decades the measure of success in congenital heart surgery was survival. That is no longer the hard part for most defects. The children who now go home in large numbers grow into a group with a recognisable pattern: developmental test scores a little below average, more difficulty with attention and language at school, and more need for extra support than their peers. Because that pattern is so consistent, advice has changed. Since 2024, the American Heart Association has recommended that every child who has open-heart surgery in the first year of life be checked repeatedly as they grow, so difficulties are found early rather than discovered in a classroom [1].

What families used to be told, and how that changed

Twenty years ago, most people assumed that if a baby with a heart defect had developmental problems later, the operation was to blame. It was a reasonable guess. Heart surgery in a newborn involves a heart–lung bypass machine, cooling the body, and hours of very careful management — plenty of moments where something could go wrong.

Then researchers began scanning babies' brains before their operations. What they found changed the field: many newborns with serious heart defects already had signs of injury in the white matter — the part of the brain that carries signals between regions — and brains that looked less mature than expected, all before a surgeon had touched them [2]. Scans done during pregnancy pushed the story back further still, showing that the brains of babies with heart defects were already somewhat smaller in the last months of pregnancy [3].

It is worth being clear about what that does not mean. It does not mean anything was done wrong. A heart built differently pumps differently, and the developing brain — the hungriest organ in the body for oxygen — notices. Nor does it mean the outcome is fixed. It means the story starts earlier than anyone thought, and that there may be more than one place to intervene.

Four studies that follow the same story from pregnancy to the toddler years

The four studies covered here each take up a different chapter of that story, and they were done in different places. A team in San Francisco followed 55 pregnancies where the baby was known to need heart surgery soon after birth [4]. A team in London compared brain scans from 116 newborns with heart defects against 127 babies born early and 360 healthy babies born at term [5]. A team in Utrecht, in the Netherlands, examined what happens during the operation itself in 83 babies [6]. And a group of 25 hospitals across North America pooled developmental testing on 868 young children [7]. Read together, they cover pregnancy, birth, the operating room, and the toddler years — the whole arc that researchers describe as a build-up of small stresses over time rather than a single injury [8].

A breathing test in pregnancy that may show how a baby's brain is coping

The San Francisco study used a test that sounds almost too simple. During a routine fetal heart ultrasound in the last third of pregnancy, the mother breathed pure oxygen through a mask for ten minutes. The sonographer then re-measured the blood flow in one of the baby's brain arteries.

The idea is that a healthy fetal brain adjusts its own blood supply moment to moment. If the vessels respond when the mother's oxygen rises, the system still has flexibility. If they do not respond at all, the brain may already be working at its limit to protect itself — an engine running flat out, with nothing left in reserve.

That is roughly what the researchers found. Among babies with hypoplastic left heart syndrome — a severe defect where the left side of the heart is underdeveloped — those whose brain vessels responded had measurably larger brains at every stage of pregnancy than those whose vessels did not. And among all the babies, those whose brain vessels had not responded were more likely to show white matter injury on a scan after birth: about one in five babies in the study had such injury. The pattern did not appear in a different defect, transposition of the great arteries, which fits what is known about how blood flows in that condition — the amount of blood reaching the brain is normal, but the oxygen it carries is low [9].

This is early work — one hospital, 55 pregnancies, and no follow-up yet on how the children developed. It is not something to ask for at your next scan. But it hints that doctors might one day identify, before birth, which babies need the closest watching.

Why a baby with a heart defect is not the same as a baby born too early

Babies born very prematurely and babies born with serious heart defects both have higher rates of developmental difficulty, so it was natural to assume their brains were affected in similar ways. The London study tested that by comparing the shapes and proportions of brain structures across all four groups.

They were not similar. The pattern in the babies with heart defects barely overlapped with the pattern in the babies born early — different regions, different signatures. That matters because protective strategies developed over the years for premature babies cannot simply be copied across.

There was also a puzzling result. At 18 to 24 months the two high-risk groups scored almost identically — a little below the healthy comparison group, but well within the range most parents would recognise as ordinary. Yet the brain scans predicted those scores in the premature babies and not at all in the babies with heart defects. Something else — genetics, the course after surgery, home and school life — appears to be doing more of the work. For families, that carries a hopeful message: a scan of your baby's brain around their due date does not tell you how they will turn out.

Something in the operating room that can be changed

The Utrecht study looked at a detail most people would never think about: salt. Blood sodium swings during heart surgery, because the fluid priming the heart–lung machine is very salty while the solution protecting the heart muscle is not. Across 83 babies and more than 2,500 measurements, the swings were large — larger, within a single operation under six hours, than doctors consider safe to change over a whole day in an adult.

Babies whose sodium swung the most showed subtle differences in the wiring of their white matter on scans afterwards. This is an association, not proof of cause; the sickest babies also received the most fluid. But the response was straightforward — the hospital now mixes certain medications in a sugar solution instead of a salty one. Some of this risk sits in ordinary, adjustable details of care rather than in the defect itself, and surgical care overall has been getting safer, with rates of brain injury after these operations falling over the past two decades [10].

Which children need developmental check-ups — more than we assumed

The largest of the four studies pooled testing on 868 toddlers from 25 hospitals. Three findings stand out.

First, average scores in cognition, language, and movement were modestly below the general-population average — roughly 88 to 91 on a scale where 100 is average and most children fall between 85 and 115. Below average as a group, but the great majority of individual children scored in the typical range.

Second, by far the strongest single factor was whether the child also had a genetic condition. About one child in nine did, and their scores were more than a full standard deviation lower. Down syndrome and 22q11.2 deletion syndrome accounted for most of that difference. This is consistent with the discovery that some of the same genes build both the heart and the brain [11].

Third — and this is the finding most likely to change what happens in clinics — children with defects usually thought of as less serious did not do better. Babies with transposition of the great arteries, who have one of the most demanding newborn operations, actually had the highest scores. Children with a repaired coarctation or tetralogy of Fallot scored slightly lower. So the old habit of offering developmental follow-up only to the sickest babies misses children who need it.

A longer hospital stay, more catheter procedures, and lower family educational level were each linked to lower scores. That last point is not a judgement about families; it identifies who most needs help getting to appointments and into early-intervention programmes. Worth knowing: only 29% of eligible children in this study came to their assessment at all, and attendance was better when the hospital booked the appointment rather than waiting for families to ask. If your child has had heart surgery, it is entirely reasonable to ask for that referral yourself.

What this means for your family

If you are expecting a baby with a heart defect, or caring for one now, a few things are worth holding onto. Some of this risk was set before birth, by how the heart formed — not by anything you did or did not do. The operation is one part of the picture, not the whole of it. Most children with heart defects develop within the normal range, even though the group average is shifted down. And the part that is most within reach is early identification: children who are picked up early and offered speech, occupational, or physical therapy do better than those found late. Ask about developmental follow-up before discharge, and keep asking, because these difficulties often become visible only as a child approaches school [12].

What researchers are working on next

Several threads run forward from here. The fetal oxygen test needs to be tried at many hospitals, with the children followed for years, before it can be used to counsel anyone. Researchers want to understand why brain scans predict development in premature babies but not in babies with heart defects, which probably means looking at genetics and at scans taken before and after surgery in the same child [13]. Perioperative sodium management is a candidate for a proper trial. And because seizures and other acute problems remain common around the time of surgery [14], teams continue to work on monitoring the brain during and after the operation. The larger shift, though, has already happened: the brain is now treated as part of heart care, from the first prenatal scan onwards and well into adulthood [15].

References

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