Waiting to Cut the Cord: What a Large New Study Means for Very Premature Babies

A plain-language look at the ABC3 trial (Knol and colleagues, Lancet Regional Health – Europe, 2024)

A large European study has tested a gentler way to handle the umbilical cord at a very premature birth: instead of clamping the cord after a set number of seconds, doctors waited until the baby was breathing well and stable before clamping. This approach did not increase the number of babies who survived without serious brain injury or a dangerous bowel problem, but it did cut the need for blood transfusions and lowered the rate of serious infections — and parents felt calmer and more content. The findings suggest the method is safe and worthwhile in hospitals set up to do it, while leaving its biggest long-term questions still to be answered [1].

Why the Timing of Cord Clamping Matters

When a baby is born, the umbilical cord still connects them to the placenta, which has been delivering oxygen and blood throughout pregnancy. For decades, the routine at most births — especially premature ones — was to clamp and cut the cord within a few seconds, so the baby could be taken to a warming table for help with breathing. That haste made sense when the priority was getting a fragile baby to the resuscitation team quickly. But it also meant the baby was cut off from a final, natural top-up of blood from the placenta.

Over the past fifteen years, researchers learned that this rush came at a cost. Studies that compared clamping immediately with waiting just 30 to 60 seconds found that the short wait reduced the number of premature babies who died in hospital — by roughly a third in some analyses [2]. A major independent review of all the evidence agreed that waiting was better than rushing, while noting that the studies differed in exactly how long they waited and how they handled the cord [3]. Because of this, "delayed cord clamping" — pausing for at least half a minute — became standard practice in many hospitals.

But waiting by the clock has a hidden assumption: that the important things happening in the baby's body have finished by the time the timer runs out. Laboratory research, much of it in newborn lambs, showed why this matters. When the cord is clamped before a baby's lungs have started working, the heart can be briefly starved of the blood it expects, followed by jarring swings in blood pressure [4]. When the baby is helped to breathe first and the cord is clamped afterward, the changeover is smoother and the brain and body get more oxygen [5]. This led to an idea: rather than waiting a fixed time, wait until the baby is actually breathing and stable. Doctors call this "physiological-based cord clamping" — clamping based on the baby's own physiology.

Putting this idea into practice safely took years of careful groundwork. An earlier British pilot study showed it was possible to start a premature baby's care while the cord was still attached [6]. At the same time, researchers learned to be careful: a different technique called "cord milking," where the cord is squeezed to push blood toward the baby quickly, had to be stopped early in one trial because it caused more bleeding in the brains of the tiniest babies than gentle waiting did [7]. Large reviews combining many studies confirmed that waiting saves lives and hinted that waiting longer might be even better, but they could not say whether waiting for the baby's body to be ready was better than simply waiting a fixed short time [8][9]. That is the gap the ABC3 trial set out to fill [10].

What the Researchers Did

The ABC3 trial took place in all nine specialist newborn-care hospitals in the Netherlands and involved 669 babies born before 30 weeks of pregnancy — about ten weeks early or more [1]. With their parents' permission given in advance, each baby was randomly assigned to one of two approaches. In the new approach, the baby was placed on a specially built trolley right next to the mother and given breathing support and warmth while still attached to the cord; the cord was clamped only once the baby was stable, meaning a steady heartbeat above 100 beats per minute and good oxygen levels without needing much extra oxygen. This waiting lasted at least 3 minutes and up to 10. In the comparison approach — the usual modern standard — the cord was clamped between 30 and 60 seconds after birth.

The main thing the researchers wanted to measure was the share of babies who survived to go home without two serious complications of prematurity: major bleeding or injury in the brain, and a severe bowel illness called necrotising enterocolitis. Importantly, both groups received good care; the comparison group was not having its cord clamped instantly, but was getting the recommended short wait. So this study asked a refined question — is waiting for the baby's body better than waiting a fixed short time? — rather than the older question of whether to wait at all.

What They Found

For the main measure, the two approaches came out essentially even. About 71 of every 100 babies in the new "wait until ready" group survived without serious brain or bowel injury, compared with about 68 of every 100 in the standard group — a difference small enough to be due to chance [1]. The rates of death, brain injury, and the bowel illness were each very similar between the two groups. On its own, that sounds like the new method made no difference.

But the fuller picture is more encouraging. Babies in the "wait until ready" group needed fewer blood transfusions, and serious bloodstream infections were less common — about 27 in 100 babies versus 33 in 100 [1]. Both of these are real, meaningful benefits: fewer transfusions means less exposure to donated blood and its small risks, and fewer infections means fewer very sick babies and shorter, less frightening hospital stays. These benefits make sense, because giving the baby more of the placenta's blood boosts their own blood and iron supply, which lowers the need for transfusions later.

It helps to understand why this gentle wait can do so much. While the cord is still attached and pulsing, the placenta keeps sending the baby a meaningful amount of blood, rich in red cells and iron. For a baby born many weeks early, whose body is not yet ready to keep up with the demands of growth, that extra blood is a head start: a higher starting level of haemoglobin, the protein that carries oxygen, and fuller iron stores to draw on in the weeks ahead. That is the most likely reason these babies needed fewer transfusions. Researchers also believe that letting the baby begin breathing before the cord is clamped lets the heart and lungs take over from the placenta smoothly, rather than in an abrupt jolt — the kind of calm transition that may matter most for the most fragile newborns.

There was one trade-off to watch. Babies in the new group arrived in the intensive care unit a little cooler on average — about 36.3°C versus 36.7°C [1]. Keeping premature babies warm is very important, so this is the main practical challenge for hospitals using the method, and it can be managed with warm wraps and careful attention to room temperature. Parents, notably, felt better with the new approach: they reported less anxiety and more contentment, likely because they could watch their baby being cared for at the bedside rather than rushed away [1]. The researchers also noticed that baby boys seemed to do better with the new method, but because this was a smaller slice of the results, they caution that it could be a chance finding and needs to be checked in future studies [1].

What This Means for Families and What Comes Next

If your baby is born very prematurely in a hospital equipped for it, this study offers reassurance that waiting to clamp the cord until your baby is breathing and stable is safe, reduces the need for transfusions and infections, and is something many parents find calmer to witness. It is not a miracle cure: it has not been shown to increase the number of babies who avoid serious brain or bowel injury compared with the standard short wait. International expert panels reflect this balance, recommending the approach only in hospitals with the right equipment, trained teams, and the ability to keep babies warm [11]. In smaller hospitals, the established practice of waiting at least 30 to 60 seconds remains a good and recommended choice.

The most important answers are still being gathered. The researchers are following these children to see how they grow and develop over the next few years. Because fewer transfusions and infections early in life could help the brain develop better later — something seen in full-term babies who had delayed cord clamping, who showed small gains in certain skills by age four [12] — these longer-term results will be the real test of whether the gentler approach helps children thrive, not just survive. For now, ABC3 marks an encouraging step: a safe, family-friendly way to give the most fragile newborns a better start, with the final verdict still to come.

References

  1. Knol R, Brouwer E, van den Akker T, et al. Physiological versus time based cord clamping in very preterm infants (ABC3): a parallel-group, multicentre, randomised, controlled superiority trial. Lancet Reg Health Eur. 2024;48:101146. doi:10.1016/j.lanepe.2024.101146 ↩
  2. Fogarty M, Osborn DA, Askie L, et al. Delayed vs early umbilical cord clamping for preterm infants: a systematic review and meta-analysis. Am J Obstet Gynecol. 2018;218(1):1–18. doi:10.1016/j.ajog.2017.10.231 ↩
  3. Rabe H, Gyte GML, Díaz-Rossello JL, Duley L. Effect of timing of umbilical cord clamping and other strategies to influence placental transfusion at preterm birth on maternal and infant outcomes. Cochrane Database Syst Rev. 2019;9(9):CD003248. doi:10.1002/14651858.CD003248.pub4 ↩
  4. Bhatt S, Alison BJ, Wallace EM, et al. Delaying cord clamping until ventilation onset improves cardiovascular function at birth in preterm lambs. J Physiol. 2013;591(8):2113–2126. doi:10.1113/jphysiol.2012.250084 ↩
  5. Polglase GR, Dawson JA, Kluckow M, et al. Ventilation onset prior to umbilical cord clamping (physiological-based cord clamping) improves systemic and cerebral oxygenation in preterm lambs. PLoS One. 2015;10(2):e0117504. doi:10.1371/journal.pone.0117504 ↩
  6. Duley L, Dorling J, Pushpa-Rajah A, et al. Randomised trial of cord clamping and initial stabilisation at very preterm birth. Arch Dis Child Fetal Neonatal Ed. 2018;103(1):F6–F14. doi:10.1136/archdischild-2016-312567 ↩
  7. Katheria A, Reister F, Essers J, et al. Association of umbilical cord milking vs delayed umbilical cord clamping with death or severe intraventricular hemorrhage among preterm infants. JAMA. 2019;322(19):1877–1886. doi:10.1001/jama.2019.16004 ↩
  8. Seidler AL, Aberoumand M, Williams JG, et al. Deferred cord clamping, cord milking, and immediate cord clamping at preterm birth: a systematic review and individual participant data meta-analysis. Lancet. 2023;402(10418):2209–2222. doi:10.1016/S0140-6736(23)02468-602468-6) ↩
  9. Seidler AL, Aberoumand M, Williams JG, et al. Short, medium, and long deferral of umbilical cord clamping compared with umbilical cord milking and immediate clamping at preterm birth: a systematic review and network meta-analysis with individual participant data. Lancet. 2023;402(10418):2223–2234. doi:10.1016/S0140-6736(23)02469-802469-8) ↩
  10. Brouwer E, Knol R, Hahurij ND, et al. Physiological-based cord clamping in very preterm infants: the Aeration, Breathing, Clamping 3 (ABC3) trial—study protocol for a multicentre randomised controlled trial. Trials. 2022;23(1):838. doi:10.1186/s13063-022-06789-6 ↩
  11. Greif R, Bray JE, Djärv T, et al. 2024 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. Circulation. 2024;150(24):e580–e687. doi:10.1161/CIR.0000000000001288 ↩
  12. Andersson O, Lindquist B, Lindgren M, et al. Effect of delayed cord clamping on neurodevelopment at 4 years of age: a randomized clinical trial. JAMA Pediatr. 2015;169(7):631–638. doi:10.1001/jamapediatrics.2015.0358 ↩