When a Baby's Two Circulations Run Side by Side

What four recent studies say about finding transposition of the great arteries before birth, getting safely through the first days, and how children do years later

Transposition of the great arteries is a heart condition present at birth in which the two main arteries leaving the heart are connected the wrong way round. Surgery to correct it is now very successful, and most children grow up well. Four recent studies look at the part that is still hard: the first few days of life, before that operation can be done.

The four studies were published between July 2025 and July 2026. One followed babies diagnosed before birth at a London hospital for as long as 27 years [1]. One asked every heart surgery unit in the United Kingdom and Ireland how they plan these births [2]. One, from two large hospitals in Türkiye, looked at what happens when the lungs' blood vessels do not open properly after birth [3]. And one, from Toronto, scanned the brains of 225 newborns before surgery to find out what kind of injury occurs and why [4]. Together they describe a condition where the surgery is no longer the frightening part — the days beforehand are.

What the condition actually is

In a heart that is formed as expected, blood returning from the body is pumped to the lungs to collect oxygen, comes back to the heart, and is then pumped out to the body — a single loop of track. In transposition the two arteries are swapped, so blood that has already delivered its oxygen is sent straight back out to the body while blood that has just collected oxygen is sent back to the lungs. Instead of one loop there are two, running side by side, and neither delivers oxygen where it is needed. A baby can only survive if some blood leaks between them.

Before birth this is not a problem, because every unborn baby has two natural openings that let blood cross over: a flap-valve hole between the heart's two upper chambers (the foramen ovale) and a short connecting vessel between the two main arteries (the ductus arteriosus). Both are supposed to close in the hours and days after birth. In a baby with transposition, they are the only thing keeping the baby alive — and they are closing.

How doctors learned to manage it

Heart conditions present at birth affect roughly nine babies in every thousand worldwide [5]. Transposition is one of the less common — and one of the most urgent, because a baby with it can become dangerously blue within hours.

The first real answer came in 1966, when two doctors in Philadelphia, William Rashkind and William Miller, described a way to enlarge the hole between the heart's upper chambers without opening the chest: a thin tube with a small balloon on the end is threaded up a vein into the heart, inflated, and pulled back through the flap-valve hole to widen it. That procedure — a balloon atrial septostomy — takes minutes, can be done at the cot side, and immediately improves mixing [6].

Ten years later, a surgeon in São Paulo named Adib Jatene described an operation that fixes the underlying problem: detaching the two great arteries, swapping them back, and moving the small coronary arteries that feed the heart muscle across with them [7]. This "arterial switch" is now the standard repair worldwide, usually done in the first week or two of life.

Then came ultrasound. In 1999 a French team showed that finding transposition on a scan before birth reduced deaths and serious illness, largely by preventing the situation where a baby goes home apparently well, the natural connections close, and the family returns in a crisis [8]. Detection before birth has improved greatly since — in the United Kingdom, from around half of affected babies before 2016 to more than four in five recently [1].

The scan cannot tell you which babies will struggle

The next question is whether the scan can also predict which babies will need emergency treatment in the first hours. Researchers have been trying since at least 2004, when a team measured the two natural openings in fetuses with transposition and found features associated with a difficult birth — but not reliably enough to plan around [9].

A large study published in 2026 has now largely settled the matter. Researchers at 23 centres enrolled 179 mother–baby pairs and analysed the 132 with complete information. Fifty of those babies (38%) became significantly short of oxygen after birth and 38 of the 50 needed an emergency balloon procedure — but no measurement on the fetal scans predicted which babies those would be [10]. Almost all did well overall: 131 of 132 went home from hospital.

For families this is important and slightly counterintuitive: a reassuring scan late in pregnancy does not mean the birth is low-risk. It means the team should prepare for every one of these births as though emergency treatment will be needed.

Where you give birth matters more than you might expect

A survey sent to all 11 heart surgery units in the United Kingdom and Ireland that operate on these babies — every one replied — shows how differently hospitals have solved this problem [2]. Just under half (five of eleven) have the maternity unit and the children's heart unit on the same site; for the others they are 0.7 to 3.6 miles apart, so a newborn has to travel. Six units plan to induce labour, three wait for labour to start naturally, and two plan a caesarean. Nearly half perform the emergency balloon procedure at the cot side or in the theatre where the birth takes place; the rest do it in a specialised X-ray room. No unit has a cardiologist standing by at every one of these births.

None of this means some units are unsafe. Each has built a workable plan around its own geography and staffing, and there is not yet enough evidence to say which is best. If you are expecting a baby with this diagnosis, it is reasonable to ask: where will I deliver, who will be there, and where would the balloon procedure happen?

The lungs have to open too

Before birth, the blood vessels in the lungs are tightly squeezed, because the lungs are not being used; at birth they are supposed to relax so blood can flow through and collect oxygen. Sometimes they do not — a condition called persistent pulmonary hypertension of the newborn. In a baby with transposition, whose oxygen levels are already fragile, this makes everything harder.

A study from two large Turkish hospitals followed 48 newborns with transposition over a single year [3]. Thirteen (about one in four) had this lung-vessel problem. They looked no different at birth, but their oxygen levels were lower and they needed far more support: on average seven days on a breathing machine instead of four, twelve days in intensive care instead of seven, twenty days in hospital instead of fourteen. All three babies who had a sudden dangerous spike in lung-vessel pressure were in this group. More of them died too, but the numbers were too small to say whether that difference was real.

The reassuring part is that it is recognisable and treatable — with a gas called nitric oxide breathed in through the ventilator, and a medicine called sildenafil to help come off it — though families should expect a longer stay.

What the brain scans showed

The Toronto team scanned the brains of 225 babies with transposition before their operation [4]. About one in ten had had a small stroke and about one in four had some injury to the brain's white matter, mostly mild; six had the pattern caused by a period of very low oxygen.

Two findings stand out. First, the balloon procedure was not associated with stroke — babies who had it were no more likely to have one. This lays to rest a worry dating back to a 2006 study suggesting the opposite [11]; later work had already pointed instead to low oxygen levels and long waits for surgery [12].

Second, in a smaller group who also had detailed blood-flow scans of the heart, the researchers found that when too much blood was going round to the lungs, less reached the rest of the body and the brain's oxygen supply fell. The six babies with low-oxygen injury split into two groups: three had been dangerously blue very early because the hole between the upper chambers was too tight, and three had gone the other way, with too much blood flooding the lungs later. Injury can come from too little mixing or too much flow. The team suggests that a baby still short of oxygen after a successful balloon procedure may be better served by bringing the operation forward than by increasing the medicine that holds the connecting vessel open — a direction, not a rule, since it has not been tested in a trial.

How children do in the long run

This is where the news is genuinely good. The London study followed 207 babies diagnosed before birth over 27 years [1]. Almost all had the switch operation, 95.5% were alive 30 days afterwards, and 92.5% of the whole group survived — many now in their twenties and thirties. About one child in eleven needed a further heart procedure, usually on the coronary or lung arteries. Around one in twenty had a neurological or developmental difficulty and about one in eighteen was diagnosed with autism: real but modest differences, and the reason development is worth watching rather than assuming a successful operation is the end of the story. Studies of adults two decades after the switch confirm that some differences in thinking skills and quality of life persist [13] — which is why follow-up through the school years is now part of good care.

What researchers are working on next

The newest idea targets the very first minute. Normally the umbilical cord is clamped soon after birth. A European group is now testing whether, in babies with transposition, it is better to leave the cord attached while the baby is given oxygen and helped to breathe, clamping only once the heart rate and oxygen levels have settled [14]. The hope is that a gentler transition makes the lung-vessel problem less likely. Results are still to come.

Until then the picture is hopeful and the focus is clear. The operation works, the scan before birth is worth having, and the effort now goes into the handful of days between being born and being repaired.

References

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  2. Jowett V, Seale AN, Carvalho JS, Hunter L, Vigneswaran T. Perinatal Management Pathways for Transposition of the Great Arteries With Intact Ventricular Septum: A National Survey. BJOG. 2026;133(1):178–180. doi:10.1111/1471-0528.18281 ↩
  3. Genc HZ, Ceylan H, Kamali H, et al. Clinical effects of persistent pulmonary hypertension in newborns diagnosed with transposition of the great arteries. Front Cardiovasc Med. 2026;13:1888066. doi:10.3389/fcvm.2026.1888066 ↩
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  10. Johnson JT, Schidlow D, Shuplock J, et al; Fetal Heart Society Research Collaborative. Fetal anatomic and physiologic predictors of neonatal hypoxia in D-transposition of the great arteries: a prospective, multicenter study by the Fetal Heart Society Research Collaborative. J Am Soc Echocardiogr. 2026. doi:10.1016/j.echo.2026.07.010 ↩
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