When Premature Lungs Also Have a Blood-Vessel Problem

What four recent studies tell families about high blood pressure in the lungs of babies with chronic lung disease of prematurity

Two problems that travel together but are not the same

Many babies born very early develop a long-term lung condition called bronchopulmonary dysplasia, and some also develop high blood pressure in the lung's blood vessels, called pulmonary hypertension. Four studies from 2025 and 2026 examined how doctors find this vessel problem, how they treat it, and what happens to these children years later. Together they suggest the lung problem and the vessel problem are more separate than their shared name implies.

Those four studies come from very different angles. One followed 320 children across 14 specialist centres in North America who had measurements taken directly inside their heart and lungs [1]. One described 18 babies at a San Francisco hospital treated with a powerful medicine for the vessels [2]. One surveyed 108 clinicians about how they actually use the ultrasound scan that makes the diagnosis [3]. And one followed 175 extremely premature babies in Wisconsin for five years after they went home [4].

What bronchopulmonary dysplasia is, and how it came to be defined by breathing support

Babies born many weeks early have lungs that have not finished building themselves: the tiny air sacs where oxygen crosses into the blood are still forming, and so are the delicate vessels wrapped around them. Keeping such a baby alive requires oxygen and breathing support, and although both are lifesaving, both also interfere with that building work. The result, first described in 1967 in babies who survived long periods on a ventilator, is a chronic lung disease lasting months or years [5].

From the beginning, doctors defined the condition by something simple to observe: how much help with breathing a baby still needs at 36 weeks, counted from the mother's last period rather than from the baby's birthday. A widely used 2001 definition sorted babies into mild, moderate and severe by oxygen requirement [6]; a 2019 update replaced it with grades 1, 2 and 3 based on the kind of support needed — a low-flow nasal cannula, a stronger non-invasive device, or a breathing tube and ventilator [7].

What none of those definitions measured was the lung's blood vessels. That was not because the vessels were thought unimportant. Ultrasound studies had already shown that vessel changes visible in the first week of life predict both chronic lung disease and later pulmonary hypertension [8], and a large 2025 analysis combining many studies found that the vessel problem affects roughly 5% of babies with mild chronic lung disease, 18% with moderate, and 41% with severe [9]. Guidelines from two major American heart and lung societies had recommended regular ultrasound checks since 2015 [10], and a 2017 expert framework described how to manage what those checks find [11]. Families already knew the stakes were real: when pulmonary hypertension persists past 36 weeks it carries a serious risk [12], and babies with both conditions come back to hospital more often in their first year [13]. Before this work, though, parents and clinicians could not answer basic questions — how severe are the vessel changes really, does a milder lung problem mean milder vessel disease, and what happens after the first year?

A milder lung problem does not mean milder vessel disease

The largest of the four studies followed children enrolled in a research registry run by the Pediatric Pulmonary Hypertension Network, a group of 14 specialist centres across North America [1]. All 320 children had been born before 32 weeks, on average at about 26 weeks and weighing around 720 grams. Sixty-nine of them had a cardiac catheterisation — a procedure in which a thin tube is threaded through a blood vessel into the heart and lungs to measure pressures directly, rather than estimating them from an ultrasound picture.

The finding that matters most for families is the one the researchers did not expect. The pressures measured inside the lungs were essentially the same whether a child's chronic lung disease had been graded 1, 2 or 3. A baby who went home on a low-flow nasal cannula could have vessel pressures just as high as a baby who needed a ventilator. The children in the study were also spread evenly across the three grades, rather than clustering in the most severe group as had been assumed.

That does not mean grade is meaningless. Most of the deaths in the study happened in children with grade 3 disease, and five years after diagnosis about 87% of that group were alive without a lung transplant, compared with 94% of the two milder groups. But the reason for the difference does not appear to be the vessel pressures themselves — it seems to lie in how poorly the sickest lungs tolerate the extra strain.

The scan everyone relies on is not applied the same way everywhere

Almost every diagnosis of pulmonary hypertension in a baby is made by echocardiography, an ultrasound scan of the heart. It is painless, can be done at the cot side, and can be repeated as often as needed. The survey of 108 clinicians — neonatologists, cardiologists, lung specialists, intensive care doctors, nurses and therapists from about 45 centres — asked how they actually use it [3].

Every single respondent said they rely on the scan. But only about half said their hospital's ultrasound laboratory has a standard, agreed way of performing it for this condition. When asked what pressure reading should raise concern, answers ranged from 25 to over 40 millimetres of mercury, with no clear majority anywhere in between. Specialists and neonatologists valued different measurements. Most respondents doubted the scan can reliably tell mild from moderate from severe, though most did trust it to tell normal from abnormal — and 90% said clearer guidelines are needed.

This is worth understanding rather than worrying about. It does not mean the scan is unreliable; it means different hospitals may describe the same finding in different words, and a repeat scan or second opinion is reasonable to ask for. It is also why many teams add a blood test — B-type natriuretic peptide, a chemical the heart releases when working too hard — alongside the scan [14].

When doctors look inside, and what they find there

Cardiac catheterisation gives the clearest answer, and an international expert group reaffirmed in 2024 that it has a place in selected children [15]. But it carries real risk: three of the 25 deaths in the registry study happened during the procedure itself [1]. It is therefore reserved for children in whom the answer will change treatment.

One thing the procedure looks for deserves special mention. Some premature babies develop narrowing of the pulmonary veins — the vessels that carry oxygen-rich blood back from the lungs to the heart. This is easy to miss on an ultrasound scan and is dangerous when present [16]; six of the 25 children who died in the registry study had it [1]. It also changes treatment, because medicines that widen the lung's arteries can do harm if the veins beyond them are blocked. If your child is being considered for vessel-widening medication, asking whether the pulmonary veins have been checked is a fair and useful question.

Treatment works better before a crisis than during one

The San Francisco study followed 18 babies given treprostinil, a medicine delivered continuously under the skin or into a vein that relaxes the lung's blood vessels [2]. All had moderate or severe chronic lung disease. Among the 11 who had repeat measurements, the average pressure in the lung arteries fell from about 46 to about 28 millimetres of mercury, and the resistance the heart had to pump against fell by more than half.

Ten of the 18 babies survived to go home. The pattern behind that number is the important part. Fourteen babies were started on the medicine as a planned step after their catheterisation, and four of those died. The other four were started on it during a sudden deterioration, as a rescue measure — and none of them survived. The authors are careful to note that their hospital also changed how it managed ventilators in 2018, and that survival improved after that change too, so the medicine is not the only thing that differed. Evidence for the other drugs used before it, including inhaled nitric oxide, also remains limited [17], and specialist teams increasingly emphasise that coordinated care across disciplines matters as much as any single prescription [18]. Still, the message for families is encouraging in one specific way: being referred early to a centre that can do these procedures is not an alarming escalation. It is the point at which treatment works best.

What the first five years actually look like

The Wisconsin study followed 175 babies born before 28 weeks who went home on oxygen; 84 of them had pulmonary hypertension at some point [4]. Two findings sit side by side, and both are worth hearing.

The first is genuinely reassuring. The vessel problem usually goes away. It resolved on ultrasound at a median of about two months from diagnosis, and among the babies who still had it when they left the neonatal unit, more than nine in ten had cleared it within a year. Deaths over five years were low and no different between the groups.

The second is more sobering. Even after the vessel pressures normalised, these children came back to hospital more often. By five years, 71% of the pulmonary hypertension group had been admitted at least once, compared with 48% of those without it, and they were admitted sooner and more times. They needed home oxygen for longer and were more likely to have had a tracheostomy, a breathing tube placed in the neck — a pattern also seen in children who go home on a ventilator [19]. The researchers' interpretation is that pulmonary hypertension is partly a marker of how fragile a baby was overall, rather than the sole cause of everything that follows.

What researchers are working on next

Three efforts follow from these studies. The first is agreeing on a single standard way to perform and report the ultrasound scan, so a diagnosis means the same thing in every hospital. The second is working out how long to keep checking: nearly one in five children in the registry study were diagnosed after their first birthday, so screening that stops at discharge misses some. The third is testing whether starting vessel medicines before a crisis genuinely improves survival, in a study large enough to separate the drug's effect from everything else that has improved in newborn care. Researchers are also following people born prematurely into adulthood, where subtle differences in the lung's blood vessels can still be measured decades later [20].

For a family in the middle of this, the practical takeaways are modest but real. A milder lung grade does not rule out a vessel problem, so it is reasonable to ask whether your baby has been screened. Ask what the scan showed and what will be repeated after discharge. Ask whether the pulmonary veins were looked at before any vessel-widening medicine is started. And know that the vessel problem itself usually resolves — while the extra care and vigilance your child needs is likely to matter for several years beyond that.

References

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