Blood Clots in Newborn Babies: What Families Need to Know

Three recent medical reports on how clots form around newborn intravenous lines, how doctors find them, and how they are treated

Blood clots are one of the lesser-known risks of newborn intensive care. They form most often around the thin plastic tubes, called central lines, that carry nutrition and medicine into a sick baby's bloodstream. Three recent medical reports examined how often these clots happen, how doctors find them, and what treatment works — and they agree on one uncomfortable point: most babies recover well, but the evidence guiding treatment is thinner than it should be.

Why a baby's blood behaves differently

To understand why clots happen in newborns, it helps to know that a baby's blood-clotting system is not simply a small version of an adult's. It is a genuinely different system. Newborns have lower levels of several proteins that help blood clot — and, at the same time, lower levels of the proteins that stop clotting from going too far. The two shortages roughly cancel each other out, so a healthy newborn is neither prone to bleeding nor prone to clotting. What that balance lacks is reserve. When a baby becomes seriously ill — with an infection, with breathing failure, with dehydration — there is very little margin, and the system can tip in either direction [1].

Add to that the equipment. Babies in intensive care almost always need a central line: a soft catheter threaded into a large vein so that fluids, nutrition and medicines can be given safely over days or weeks. Without one, many extremely premature babies could not be fed at all. But any tube inside a blood vessel slows the flow of blood around it, can irritate the vessel wall, and gives clotting a place to begin. The great majority of clots in newborns start this way.

How doctors' understanding developed

For most of medical history, clots in newborns were thought to be vanishingly rare. That changed when doctors began collecting cases systematically. The Canadian Registry of Venous Thromboembolism, which gathered reports from paediatric centres beginning in 1990, was among the first efforts to count these events properly, and it revealed a pattern that still holds today: clots in childhood cluster in the first month of life, and central lines are the single biggest reason [2].

Counting, however, is not the same as knowing what to do. For thirty years the field accumulated better and better descriptions of the problem while running almost no trials comparing one treatment with another. That is why, as the 2026 review by Dr Rozeta Sokou and colleagues at the University of Athens and partner hospitals in Greece, the United Kingdom and Italy explains, doctors treating a newborn's clot today are largely working from experience, expert consensus, and studies done in older children and adults [1]. Two other recent reports try to add real data to that thin foundation: a study of 122 newborns treated with an oral blood thinner at a hospital in Fujian, China [3], and a detailed account of two babies with clots inside the heart itself, treated at the "Bambino Gesù" Children's Hospital in Rome [4].

How common are these clots?

The honest answer is that it depends on how hard you look. When Dutch researchers set out to find every case in the country over a five-year period — a study they called NEOCLOT — they found roughly 4 clots for every 1,000 babies admitted to neonatal intensive care. Of the 115 babies identified, 79% had been born prematurely [5]. Other studies report anywhere from about 2 to about 38 per 1,000 admissions, and the range mostly reflects differences in how often units scan for clots rather than real differences between hospitals [1]. Many clots cause no symptoms at all and are found by chance during an ultrasound done for another reason.

When a clot does cause symptoms, the signs are usually local: a line that stops working, swelling of an arm, leg or the side of the neck, or a change in the colour or temperature of a limb. Doctors confirm the diagnosis with an ultrasound scan — the same painless, radiation-free technology used during pregnancy, performed at the cot side.

What the treatment study found

Blood thinners, called anticoagulants, are the mainstay of treatment. For years the standard has been low-molecular-weight heparin, a drug given by injection under the skin, usually twice a day, with regular blood tests to check the dose. It works, but for a baby it means repeated needles, and for parents it means watching that happen.

The study from Fujian tested an alternative: rivaroxaban, a blood thinner that can be given by mouth. The researchers reviewed the records of 122 newborns with line-related clots treated between March 2022 and October 2024. The doses followed a schedule worked out in a large international children's trial known by the name EINSTEIN-Jr (a randomised study of body-weight-adjusted rivaroxaban in children), in which the smallest patients receive the medicine three times a day [6].

The results were encouraging. After six weeks of treatment, the clot had disappeared completely in 71% of babies — 87 out of 122. When treatment continued to three months, that figure rose to 89%, or 108 out of 122. No baby in the study had a bleeding problem, an allergic reaction, or a clot that came back [3].

Two other findings are practically useful. Clots around implanted ports — a type of long-term device placed fully under the skin — cleared less often (67%) than clots around ordinary central lines (93%). And when the line had been difficult to insert, meaning two or more attempts at the same spot, the clot was much less likely to clear completely. The researchers suggest a straightforward explanation: each extra attempt causes a little more damage to a very small, very delicate vein.

Why the good news comes with caution

It would be easy to read those numbers as proof that the oral medicine is better. The researchers themselves are careful not to say that, and families deserve the same care.

This was a look back at records from a single hospital, not a trial. There was no comparison group receiving the older injected medicine at the same time. Only 15 of the 122 babies had been born prematurely — yet premature babies are both the most likely to develop clots and the most vulnerable to bleeding, so the group least represented is the group where the answer matters most. And while no bleeding occurred, 122 babies followed for about three months is simply too small a study to detect uncommon complications. For comparison, the Dutch NEOCLOT study found serious bleeding in 9 of 115 babies (about 8%) — though notably, five of those bleeds came from the small catheter used to give the injections rather than from the medicine's effect on the blood [5]. Injections, in other words, carry risks of their own, which is part of why an oral option is worth pursuing.

Guidance from specialist societies reflects this uncertainty carefully. Recommendations published in 2018 by the American Society of Hematology were almost all rated as based on very low certainty evidence [7], and an updated version published in 2025 addressed oral blood thinners in children for the first time [8]. Even so, injected heparin remains the recommended first choice for newborns, because premature babies were left out of the trials that led to the oral medicine's approval [1]. Practical instructions on giving heparin safely to newborns still come mostly from expert experience rather than trials [9].

The two babies with clots in the heart

The Rome report describes something rarer and, for parents, reassuring in its outcome. Both babies had a clot inside a chamber of the heart. The first was a full-term girl who had inhaled meconium — the baby's first stool — during birth, and whose clot was visible on a heart scan within an hour of delivery. Because it appeared so quickly, the doctors concluded it had probably begun forming before she was born, driven by inflammation rather than by any tube. She was treated with injected heparin, and the clot had gone within five days. Later testing showed she had inherited a gene variant that mildly increases clotting risk, the same one her mother carried. The second baby, born at 36 weeks, was severely anaemic at birth and developed a small clot in the left side of her heart on day seven; hers dissolved within about a week of starting treatment [4].

Neither baby suffered a complication from the clot or from the medicine. The doctors' broader message is about vigilance: heart clots can be easy to miss, so scans should be done carefully from several angles, and a very sick term baby with inflammation deserves a close look even without a line in place.

What this means for your family, and what comes next

If your baby has been found to have a clot, several things are worth holding on to. Clots are a recognised complication of the lines that keep very sick babies alive, not a sign that anything went wrong in their care. Most clots dissolve, either on their own or with treatment. The main risk of treatment is bleeding, which is why the team will check blood tests and perform an ultrasound scan of the head before starting a blood thinner. And prevention matters more than treatment: careful line placement, ultrasound guidance during insertion, and removing lines as soon as they are no longer needed all reduce risk [10].

Researchers are working on several fronts. Studies of large hospital databases are tracking how often clots occur and in whom [11], and a 2026 analysis pooling many studies identified pre-eclampsia in pregnancy, low birth weight, heart defects and infection as the clearest risk factors — while finding no blood test yet reliable enough to predict who will develop a clot [12]. Clots in arteries, which are less common but can affect blood flow to a limb, are being studied separately [13]. What all three of the reports covered here call for is the same thing: proper trials, run across many hospitals, that include premature babies and follow children for years rather than months. Until those exist, the teams caring for your baby are making thoughtful, individualised judgements — and it is entirely reasonable to ask them to explain the reasoning behind each one.

References

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  2. Andrew M, David M, Adams M, et al. Venous thromboembolic complications (VTE) in children: first analyses of the Canadian Registry of VTE. Blood. 1994;83(5):1251–1257. doi:10.1182/blood.V83.5.1251.1251 ↩
  3. Zhang R, Chen G, Cai WH, Yang B, Lin YF, Zhan TH. Efficacy and safety of rivaroxaban in neonatal catheter-related thrombosis: a single-center retrospective study of 122 cases. PeerJ. 2025;13:e20375. doi:10.7717/peerj.20375 ↩
  4. De Rose DU, Mecarini F, Campanale CM, et al. Management of intracardiac thrombosis in newborns: a case series and a narrative review of the literature. Front Cardiovasc Med. 2025;12:1659312. doi:10.3389/fcvm.2025.1659312 ↩
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  6. Male C, Lensing AWA, Palumbo JS, et al. Rivaroxaban compared with standard anticoagulants for the treatment of acute venous thromboembolism in children: a randomised, controlled, phase 3 trial. Lancet Haematol. 2020;7(1):e18–e27. doi:10.1016/S2352-3026(19)30219-430219-4) ↩
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