Finding a Hidden Heart Problem Before Birth: The Veins That Join the Wrong Side of the Heart

What new research on computer-assisted pregnancy scans, and long-term follow-up of children after surgery, means for families

Total anomalous pulmonary venous connection is a rare heart difference in which the veins carrying oxygen-rich blood back from the lungs join the wrong side of the heart. Surgery can repair it, but babies do far better when it is found on an ultrasound scan before birth — and it is one of the hardest heart conditions to see on a scan. New research is testing whether computer software can help.

A plumbing problem, and why the timing of the diagnosis matters so much

In a heart that has formed normally, four veins carry blood back from the lungs, freshly loaded with oxygen, and empty into the left side of the heart. From there the left side pumps that oxygen-rich blood out to the brain, the kidneys, the muscles — everywhere. In total anomalous pulmonary venous connection, usually shortened to TAPVC, those four veins never make that connection. Instead they join together into a shared channel that drains into the right side of the heart, where the used, oxygen-poor blood collects. Oxygen-rich and oxygen-poor blood mix, and the baby is left with less oxygen than she should have.

This can be repaired with an operation, and most children who have that operation do well. What makes TAPVC unusual among heart conditions is how much depends on when it is found. In some babies, the shared channel is narrowed, so blood backs up into the lungs — doctors call this obstruction. Those babies become very unwell within hours of birth. And here is the difficulty: an obstructed baby looks almost exactly like a baby with a different, more common newborn lung problem, one that is treated with a breathing tube, extra oxygen and a gas called nitric oxide. Those treatments help the common problem and can make TAPVC worse. The safest situation by far is one in which everyone already knows the diagnosis, the baby is born in a hospital with heart surgeons, and the plan is written down before labour begins.

What families used to face, and what has changed

For most of the last century, TAPVC was discovered only after a baby became blue or breathless, often after going home. A large study gathering cases across the United Kingdom, Ireland and Sweden helped establish what actually determines how children do: which type of TAPVC a child has, whether the veins are obstructed, and whether there are other heart problems alongside it [1]. Surgical results improved steadily over the decades. Detection before birth did not improve nearly as much. A recent national study from Denmark noted that as few as 2.4% of cases are picked up on pregnancy scans, which means the great majority of families still learn the diagnosis after their baby is born and unwell [2].

Why this heart difference is so hard to see on a pregnancy scan

The pulmonary veins are tiny — thinner than a strand of spaghetti in a mid-pregnancy fetus — and they drift in and out of view as the sonographer sweeps the probe across the chest. Confirming that all four of them arrive in the correct chamber is one of the hardest things to do in obstetric ultrasound, and most scans are not performed by heart specialists.

So researchers took a different approach: instead of hunting for the veins, look for the space they leave behind. When the veins do not join the left upper chamber, a shared channel sits behind that chamber, pushing it slightly forward and widening the gap between the heart and the large artery running down the back of the chest. Two measurements of that gap have been developed and tested — one published in 2014 that compares the gap to the width of that artery [3], and one published in 2023 that compares it to the size of the chamber in front of it [4]. Both are taken from the standard four-chamber picture of the heart that every routine anomaly scan already includes. The catch is that the measurement depends entirely on exactly where the person scanning places two small points on the screen — and small differences in placement change the answer.

A case published from Poland shows the pathway working as it should. A heart problem was suspected at a routine 20-week scan, the mother was referred to a specialist prenatal cardiology centre, three detailed fetal heart scans were done through the pregnancy, and the birth was planned by caesarean section at the hospital with the surgical team. Medication to keep a vital blood vessel open was started in the delivery room, and the baby's heart was repaired on the seventh day of life [5].

Teaching a computer to take the measurement

Two studies from Showa Medical University Hospitals in Tokyo, published in January and July 2026, asked whether software could do the measuring. In the larger of the two, the researchers collected heart scan videos from 203 pregnancies — 172 where the baby's heart was normal, 25 where the baby had a different heart condition, and six where the baby had TAPVC. They built a program that finds the right frame of the video on its own and then takes both measurements, with no human placing any points [6].

They then ran a fair test. Twenty doctors — three specialists certified in fetal heart scanning, eight more experienced trainees and nine junior trainees — looked at the same twenty videos and took the measurements themselves. The specialists were outstanding and clearly better than the software. But the software beat both groups of trainees, and by a wide margin. That matters more than it might sound, because in almost every health system in the world, routine pregnancy scans are done by sonographers and general obstetric doctors, not by fetal heart specialists. Raising the floor is what changes how many babies are found.

The companion study went after the harder target: seeing the connection itself. Using scans from 106 pregnancies, the team trained software to trace the pulmonary veins and the left upper chamber through a three-dimensional reconstruction, then measured how far apart they were and at what angle. In babies with normal hearts, the vein and the chamber essentially touched; in babies with TAPVC, they were clearly separated — the difference a computer could measure [7].

Both studies come with a large caveat, and the researchers say so plainly. Each included only six babies with TAPVC, because the condition is rare. Both used one hospital's scanners from one manufacturer. This is promising early work, not a tool available in clinics.

How children do after the operation

Families rightly want to know what comes after surgery. Two studies published in 2025 give an unusually honest picture.

The Danish study followed every child in the country born with TAPVC between 2000 and 2018 — 89 children among nearly 1.2 million births [2]. Sixty-five had the repair operation, most of them in the first month of life. Of those, 88 out of 100 were alive three months after surgery and 78 out of 100 were still alive twenty years later. The children who needed a second operation, usually within a few months of the first, did considerably worse. Babies born prematurely also faced a higher risk. The study also found that children who had been repaired were more likely than other children to have other long-term health conditions and to have been seen for emotional or behavioural difficulties — 26 out of 100 compared with 6 out of 100 for other health conditions, and 8 out of 100 compared with 3 out of 100 for emotional or behavioural ones. The authors are careful to say the numbers are small and need confirming elsewhere, but it is a good reason for regular follow-up beyond the heart clinic.

A study of 48 children operated on over ten years at two hospitals in Fujian, China, added the detail of who is most at risk [8]. Babies whose veins were already narrowed before surgery did substantially worse than those whose veins were open, and babies with a smaller left upper heart chamber also did worse. This is why doctors look so carefully at those two things on the scans before an operation.

What this means for your family

If TAPVC has been found during your pregnancy, that is genuinely good news within difficult news, because it means the plan can be built in advance: delivery at a hospital with a heart surgery team, a neonatal team who know what to expect, and no delay in getting to the operating room. Research from settings with fewer resources shows the same thing from the other direction — getting babies to a surgical centre early improves how they do [9], and hospitals that join up their pregnancy and newborn heart services report better results after newborn heart surgery [10].

It is also worth knowing that surgeons are still comparing techniques rather than having settled on one. A seventeen-year review from a single centre in Malaysia found no clear difference between two approaches to the repair, and instead found that how well the baby was doing before surgery mattered most [11]. What doctors watch for afterwards is narrowing of the repaired veins, and there is active work on preventing it — including a study of a blood-pressure medicine given after surgery [12] and programmes that scan the veins on a fixed schedule so that narrowing is caught before a child becomes unwell [13].

What researchers are working on next

Three things. The first is testing the computer-assisted measurements in many hospitals, on different brands of ultrasound machine, and in far more pregnancies — the only way to know whether they work outside the centre that built them. The second is connecting detection to outcome: no study has yet shown that software-assisted scanning actually results in more babies being born at a hospital with a surgeon ready. The third is the veins themselves — finding ways to stop them narrowing after repair, because that, more than the first operation, is what shapes the long years afterwards. None of that is finished. But for the first time, the problem of finding TAPVC before birth is being worked on with the same seriousness as the problem of fixing it.

References

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  2. Henningsen MB, Bohnstedt C, Vestergaard TR, et al. Nationwide registry study of long term survival and comorbidities in total anomalous pulmonary venous connection in Denmark. Sci Rep. 2025;15(1):30408. doi:10.1038/s41598-025-15769-0 ↩
  3. Kawazu Y, Inamura N, Shiono N, et al. 'Post-LA space index' as a potential novel marker for the prenatal diagnosis of isolated total anomalous pulmonary venous connection. Ultrasound Obstet Gynecol. 2014;44(6):682–687. doi:10.1002/uog.13357 ↩
  4. Anuwutnavin S, Unalome V, Rekhawasin T, et al. Fetal left-atrial posterior-space-to-diagonal ratio at 17–37 weeks' gestation for prediction of total anomalous pulmonary venous connection. Ultrasound Obstet Gynecol. 2023;61(4):488–496. doi:10.1002/uog.26072 ↩
  5. Witkowski S, Węgrzynowski J, Krekora M, et al. Total anomalous pulmonary venous connection – prenatal echocardiography and neonatal follow-up. J Ultrason. 2025;25(101):20250012. doi:10.15557/jou.2025.0012 ↩
  6. Aoyama R, Harada N, Komatsu M, et al. Fully automated biometric parameter measurement in prenatal ultrasound screening for total anomalous pulmonary venous connection. Bioengineering (Basel). 2026;13(7):822. doi:10.3390/bioengineering13070822 ↩
  7. Komatsu R, Komatsu M, Takeda K, et al. Three-dimensional visualization and detection of the pulmonary venous–left atrium connection using artificial intelligence in fetal cardiac ultrasound screening. Bioengineering (Basel). 2026;13(1):100. doi:10.3390/bioengineering13010100 ↩
  8. Xue X, Ling W, Wu Q, et al. Prognostic factors in pediatrics TAPVC: a 10-year retrospective study. Sci Rep. 2025;15(1):11734. doi:10.1038/s41598-025-94619-5 ↩
  9. Singh G, Parmar D, Surti J, et al. Timing of transfer to a tertiary care center and early surgical outcome of obstructed total anomalous pulmonary venous connection in resource-limited settings. Ann Pediatr Cardiol. 2025;18(3):244–251. doi:10.4103/apc.apc_202_24 ↩
  10. Sun Y, Han Y, Li G, et al. Prenatal-postnatal integrated management model improves outcomes of neonatal cardiac surgery in critical congenital heart disease: a retrospective cohort study. BMC Pediatr. 2026;26(1):6. doi:10.1186/s12887-025-06378-x ↩
  11. Singh G, Mazalan SL, Ramachandran S, et al. Total anomalous pulmonary venous drainage: overall results, comparison of the sutureless versus the conventional approach, and predictors of adverse events – a 17-year single-center experience. Ann Pediatr Cardiol. 2026;19(4):389–395. doi:10.4103/apc.apc_153_25 ↩
  12. Shentu J, Zhang M, Xu Z, et al. Valsartan to prevent acquired pulmonary vein stenosis in pediatric patients after total anomalous pulmonary venous connection surgery. J Am Heart Assoc. 2025;14(4):e036911. doi:10.1161/JAHA.124.036911 ↩
  13. Saini A, Jergel A, Xiang Y, et al. Impact of structured surveillance and intervention on long-term vein outcomes in pediatric pulmonary vein stenosis. Children (Basel). 2026;13(7):933. doi:10.3390/children13070933 ↩