A Baby's Own Blood: Fetal Haemoglobin, Transfusions and the Health of Very Premature Babies

What three 2026 studies from the Netherlands, Austria and the United States (van Daelen et al., Suppan et al. and Zeiler et al.) tell families about fetal haemoglobin, blood transfusions and serious eye disease

Before birth, a baby's blood carries mostly fetal haemoglobin, a form of the oxygen-carrying protein that holds on to oxygen tightly. New research shows that even very premature babies are born with mostly fetal haemoglobin, that blood transfusions from adult donors replace it faster, and that faster loss goes along with serious eye and lung problems, although this does not prove that transfusions cause them.

Many parents of a very premature baby hear the word "transfusion" within the first days in the neonatal intensive care unit (NICU), the hospital ward that cares for sick and premature newborns. Transfusions are a common and often life-supporting part of that care. This article explains what three studies published in 2026 add to our understanding: a large study from Rotterdam in the Netherlands [1], a careful study of oxygen levels in the brain from Graz in Austria [2], and a review of babies with serious eye disease from Utah in the United States [3].

Why the type of haemoglobin in a baby's blood matters

Haemoglobin is the protein inside red blood cells that picks up oxygen in the lungs and drops it off in the rest of the body. Before birth, a baby makes mostly fetal haemoglobin (often shortened to HbF). It grips oxygen tightly, which suits life in the womb, where oxygen is scarce. Adults make adult haemoglobin (HbA), which lets go of oxygen more easily. After birth, a baby's body slowly switches from making the fetal kind to the adult kind over many weeks.

Very premature babies often need red blood cell transfusions, because they are born before their bodies can make enough blood and because small blood samples are taken for tests. Donated blood comes from adults, so every transfusion replaces some of the baby's fetal haemoglobin with adult haemoglobin. Researchers have wondered whether this quicker switch might expose delicate, still-developing tissues to more oxygen than is good for them. One concern is retinopathy of prematurity (ROP), an eye condition in which blood vessels at the back of the eye grow abnormally; severe ROP can need laser or injection treatment to protect sight. Another is bronchopulmonary dysplasia (BPD), a long-lasting lung condition.

How doctors and researchers came to ask this question

Scientists have studied the switch from fetal to adult haemoglobin for many years [4]. In the 1970s, a researcher showed that premature babies switch at the same pace they would have done in the womb; being born early does not speed it up [5]. Transfusions, however, change the balance very quickly. In a small study of 11 babies born at 27 weeks of pregnancy or earlier, a transfusion lowered fetal haemoglobin from about 93% of the total to about 43%, and the blood let go of oxygen more easily afterwards [6]. Fetal and adult red blood cells differ in other ways too, including their shape and how long they last [7].

For years, the main question doctors asked about transfusions was "at what blood level should we give one?" Large trials in the United States and Europe found that waiting until the blood level is lower did not lead to more deaths or disability than transfusing earlier, so a more cautious approach is known to be safe [8][9]. Even so, in a study of 64 NICUs across 22 European countries, about 37 in every 100 babies born before 32 weeks still had a transfusion in their first four weeks [10].

Meanwhile, researchers noticed a pattern. In Sweden, babies born before 30 weeks who had less fetal haemoglobin in their first week were more likely to develop ROP [11] and BPD [12]. In Germany, a study of more than 12,000 very premature babies found that those who had transfusions were more likely to develop ROP needing treatment [13]. These studies could not show cause and effect, but they raised a hopeful idea: what if transfusions could use blood that is rich in fetal haemoglobin? Blood collected from the umbilical cord after a healthy full-term birth is exactly that. Before 2026, though, large up-to-date studies describing normal fetal haemoglobin levels at each stage of pregnancy and how fast they fall after premature birth were scarce, and nobody knew how many babies with severe ROP had actually been transfused.

What the Dutch study found about normal levels and transfusions

Doctors at the Sophia Children's Hospital in Rotterdam looked back at routine blood-gas results, which their NICU already collects for care, from babies admitted between 2020 and 2024; no extra blood was taken for the study [1]. In 856 newborns who had not yet had a transfusion, fetal haemoglobin typically made up about 85% or more of all haemoglobin on the day of birth for babies born between 24 and 35 weeks of pregnancy. It was lower in babies born closer to full term, about 74% at 40 weeks.

They then followed 458 babies born before 30 weeks. On average, fetal haemoglobin fell during the first weeks in every age group, fastest in the earliest-born babies, at 24 or 25 weeks. These babies also had the most transfusions: about 92 in every 100 babies born at 24 or 25 weeks were transfused, compared with about 25 in every 100 born at 28 or 29 weeks. Babies who were never transfused kept fetal haemoglobin above about 75% of their total, whereas in babies who had four or more transfusions it dropped to about 17% at its lowest. The drop was visible even after one transfusion.

Babies who went on to develop ROP needing treatment (51 of the 458) or severe BPD (121 of the 458) lost their fetal haemoglobin faster. As a group, babies who had at least one serious problem (severe eye, lung or bowel disease, or death before going home) had started with similar levels at birth to babies who had none. The doctors stress that this shows a link, not proof that losing fetal haemoglobin causes these illnesses.

What the Austrian study found about oxygen in the brain

In Graz, a team followed 50 stable newborns who never needed a transfusion: 25 born moderately early, on average at about 33½ weeks, and 25 born at full term [2]. All weighed at least 1,500 grams (about 3.3 pounds). Three times over the first 18 days, the team measured fetal haemoglobin from small blood samples and used near-infrared spectroscopy (NIRS), a painless light sensor placed on the forehead, to estimate how much oxygen the brain tissue had.

At any single moment, a baby's fetal haemoglobin level did not predict the brain oxygen reading. But when the researchers looked at changes within the same baby, a larger natural fall in fetal haemoglobin between the first few days and days 5 to 10 went with a small rise in brain oxygen. The effect was small, and the authors describe it as a starting point for more research, especially in smaller babies who receive transfusions.

What the American study found about babies with serious eye disease

In Utah, doctors in five hospitals of one health system reviewed every baby born before 29 weeks of pregnancy between 2021 and 2024 who developed severe ROP, which they defined as stage 3 or worse [3]. There were 34 such babies, and all of them survived to go home. Thirty-two of the 34 had received red blood cell transfusions from adult donors, between 1 and 18 each, and eight had their first transfusion on the very day they were born. Only two had never been transfused. These hospitals already used careful rules to limit transfusions.

The authors conclude that changing the kind of blood used could not prevent every case of severe ROP, because some babies develop it without any transfusion. But because most affected babies were transfused, often very early, cord-blood transfusions might help many of them, and the cord blood would need to be collected and stored before these babies are born.

What this means for your baby

If your baby needs a transfusion, it is because the medical team judges that your baby needs more red blood cells, and that remains important care. These studies do not suggest refusing or delaying a transfusion that doctors recommend. They do support things many NICUs already do to reduce the need for transfusions, such as waiting a short time before clamping the umbilical cord at birth, taking only the blood samples that are truly needed, and following careful transfusion rules; the Utah hospitals, for example, use all of these [3]. It is always reasonable to ask your baby's team how they try to limit blood tests and transfusions, and how they check your baby's eyes for ROP.

What researchers are working on next

The big question is whether giving cord blood instead of adult blood actually prevents eye and lung disease. The Umbilical or Adult Donor Red Blood Cells in Extremely Low Gestational Age Neonates and Retinopathy of Prematurity (BORN) trial, carried out in eight hospitals across eight regions of Italy, tested this idea. Overall, it found no clear difference, but about 43 in every 100 babies in the cord-blood group also received adult blood. Among babies who received only the blood they were assigned, none of the 17 cord-blood babies developed severe ROP, compared with about 34 in every 100 of the 38 babies given adult blood [14]. You can read more in our article on the BORN trial. In Utah, researchers have shown that cord blood collected locally could, in principle, cover these babies' needs [15], and they are planning a new trial in which cord blood will be collected from volunteer mothers at the time of healthy full-term births [16].

A hopeful bottom line

Very premature babies are born with blood that is rich in their own fetal haemoglobin. Transfusions, though often necessary, replace it faster, and faster loss is linked with serious eye and lung problems. Researchers are now testing whether transfusions made from umbilical cord blood can protect premature babies' eyes and lungs, and families can take comfort that these questions are being studied carefully.

References

  1. van Daelen JH, Gangaram-Panday NH, Huisman EJ, et al. Gestational age references and trajectory of fetal haemoglobin in relation to outcome in neonates born before 30 weeks of gestation: a single-centre retrospective cohort study in The Netherlands. EClinicalMedicine. 2026;100:104256. doi:10.1016/j.eclinm.2026.104256 ↩
  2. Suppan E, Suppan T, Schwaberger B, et al. Postnatal Changes in Fetal Hemoglobin and Tissue Oxygenation in Preterm and Term Neonates: A Prospective Observational Study. Neonatology. 2026:1-10. doi:10.1159/000553520 ↩
  3. Zeiler BB, Hartnett ME, Addams JL, et al. Transfusion Histories of Neonates Who Developed Severe Retinopathy of Prematurity. Neonatology. 2026:1-6. doi:10.1159/000551673 ↩
  4. Sankaran VG, Orkin SH. The switch from fetal to adult hemoglobin. Cold Spring Harb Perspect Med. 2013;3(1):a011643. doi:10.1101/cshperspect.a011643 ↩
  5. Bard H. Postnatal fetal and adult hemoglobin synthesis in early preterm newborn infants. J Clin Invest. 1973;52(8):1789-1795. doi:10.1172/JCI107360 ↩
  6. De Halleux V, Truttmann A, Gagnon C, Bard H. The effect of blood transfusion on the hemoglobin oxygen dissociation curve of very early preterm infants during the first week of life. Semin Perinatol. 2002;26(6):411-415. doi:10.1053/sper.2002.37313 ↩
  7. Pellegrino C, Stone EF, Valentini CG, Teofili L. Fetal Red Blood Cells: A Comprehensive Review of Biological Properties and Implications for Neonatal Transfusion. Cells. 2024;13(22):1843. doi:10.3390/cells13221843 ↩
  8. Kirpalani H, Bell EF, Hintz SR, et al. Higher or Lower Hemoglobin Transfusion Thresholds for Preterm Infants. N Engl J Med. 2020;383(27):2639-2651. doi:10.1056/NEJMoa2020248 ↩
  9. Franz AR, Engel C, Bassler D, et al. Effects of Liberal vs Restrictive Transfusion Thresholds on Survival and Neurocognitive Outcomes in Extremely Low-Birth-Weight Infants: The ETTNO Randomized Clinical Trial. JAMA. 2020;324(6):560-570. doi:10.1001/jama.2020.10690 ↩
  10. Houben NAM, Fustolo-Gunnink S, Fijnvandraat K, et al. Red Blood Cell Transfusion in European Neonatal Intensive Care Units, 2022 to 2023. JAMA Netw Open. 2024;7(9):e2434077. doi:10.1001/jamanetworkopen.2024.34077 ↩
  11. Hellström W, Martinsson T, Morsing E, Gränse L, Ley D, Hellström A. Low fraction of fetal haemoglobin is associated with retinopathy of prematurity in the very preterm infant. Br J Ophthalmol. 2022;106(7):970-974. doi:10.1136/bjophthalmol-2020-318293 ↩
  12. Hellström W, Martinsson T, Hellstrom A, Morsing E, Ley D. Fetal haemoglobin and bronchopulmonary dysplasia in neonates: an observational study. Arch Dis Child Fetal Neonatal Ed. 2021;106(1):88-92. doi:10.1136/archdischild-2020-319181 ↩
  13. Glaser K, Härtel C, Dammann O, et al. Erythrocyte transfusions are associated with retinopathy of prematurity in extremely low gestational age newborns. Acta Paediatr. 2023;112(12):2507-2515. doi:10.1111/apa.16965 ↩
  14. Teofili L, Papacci P, Pellegrino C, et al. Cord red blood cell transfusions for severe retinopathy in preterm neonates in Italy: a multicenter randomized controlled trial. EClinicalMedicine. 2025;87:103426. doi:10.1016/j.eclinm.2025.103426 ↩
  15. Christensen RD, Bahr TM, Christensen TR, et al. Banked term umbilical cord blood to meet the packed red blood cell transfusion needs of extremely-low-gestational-age neonates: a feasibility analysis. J Perinatol. 2024;44(6):873-879. doi:10.1038/s41372-023-01833-y ↩
  16. Bahr TM, Ohls RK, Christensen TR, et al. Three studies needed to inform the design of the U-BET (umbilical cord blood for extremely low-gestational-age transfusions) clinical trial. J Perinatol. 2026;46(1):55-60. doi:10.1038/s41372-025-02345-7 ↩