Tiny Kidneys, Growing Brains: What a Large Study Found About Kidney Injury in Very Premature Babies

A plain-language look at new research connecting early kidney problems to later development in babies born extremely early

A large US study of 660 children who were born extremely prematurely found that those who had a sudden kidney problem in their first weeks of life were more likely, two years later, to have delays in thinking and learning [1]. About 4 in 10 of these babies had such kidney injury, and after accounting for other risk factors, that group had roughly double the chance of a low score on a standard developmental test. The researchers are careful to say this is a link, not proof that the kidney problem caused the delays — but it means kidney injury is worth watching closely.

Why This Question Matters

Babies born extremely early — around 24 to 27 weeks into pregnancy, when a full-term pregnancy is 40 weeks — are among the most fragile patients in any hospital. Over the past few decades, doctors have become much better at helping these tiny infants survive. But survival is only half the story: the rate of serious long-term complications has barely improved, even as more babies live [2]. For families, the biggest worry is usually how their child will develop — whether they will walk, talk, learn, and thrive like other children. Doctors group these concerns under the term "neurodevelopmental impairment," which simply means difficulties with thinking, movement, hearing, or vision, and it remains one of the most common challenges faced by children who were born very early [3].

Because of this, researchers are hunting for things that happen in the first days of life that might be changed to give babies a better start. One promising suspect is the kidney. The kidneys filter waste from the blood, and in a premature baby they are still developing and easily stressed. When they suddenly stop working well — a condition doctors call acute kidney injury, or AKI — it can be a sign that the whole body is under strain.

How Common Is Kidney Injury, and Why Look at the Brain?

Until recently, doctors did not have a good way to count how often kidney injury happened in newborns. Once a standard definition was agreed upon, the answer surprised many people: kidney injury is not rare at all. A large international study found it is common in intensive-care nurseries and is linked to babies staying in the hospital longer and, sadly, to a higher chance of dying [4]. Among the most premature babies specifically, close to 40% experience some degree of kidney injury [5].

Why would a kidney problem have anything to do with the brain? It turns out the body's organs are deeply connected. When the kidneys are injured, they can release signals that cause inflammation throughout the body — including, potentially, the brain. Earlier research had already hinted at a connection: some very premature babies with early kidney injury showed differences on brain scans taken around their original due date [6], and a smaller study had suggested that children who survived kidney injury tended to have poorer development [7]. What was missing was a big, carefully followed group of children in which the question could be studied properly. That is what this new research provided.

How the Study Worked

The researchers did something clever and responsible: instead of starting a brand-new study, they reused information from an earlier, very well-run clinical trial called PENUT. That trial had originally tested whether a hormone called erythropoietin could protect premature babies' brains. It did not help — but along the way, the trial gathered detailed, high-quality records on 941 babies at 30 hospitals across the United States, and it checked in on the children at about two years of age using a standard developmental assessment [8].

For this new analysis, the team focused on the 660 children who survived and came back for their two-year check-up [1]. They looked at which babies had experienced kidney injury early in life, and then compared the two-year development of those who had kidney injury with those who did not. Importantly, they used statistics to account for the fact that the babies with kidney injury were, on average, born a bit earlier and smaller and had a rougher start — so the comparison would be as fair as possible.

What They Found

Among the children who survived, about 39% had experienced kidney injury. Those children had, after fair comparison, meaningfully higher odds of a combined outcome the researchers called "death or moderate-to-severe developmental impairment" — the numbers work out to roughly a 50% increase in the odds [1]. The clearest signal was in thinking and learning skills: children who'd had kidney injury were nearly twice as likely to have a low score in the cognitive part of the test, and more than twice as likely to have a very low score.

A few details help put this in perspective. The connection did not depend on how severe or how early the kidney injury was — even milder kidney injury was linked to lower thinking-and-learning scores. And after the fair comparison, kidney injury by itself was not clearly linked to a higher chance of dying, nor to movement (motor) problems specifically. In other words, the strongest and most consistent link was between kidney injury and later cognitive development.

One way to picture "higher odds" is this: imagine two groups of children who are otherwise similar, except that one group had kidney injury as newborns. In that group, somewhat more children than expected showed developmental delays in thinking skills — not all of them, and not even most of them, but enough that the pattern stood out clearly once the researchers did the math [1]. It is the difference between a raised risk and a certainty. Many children who had kidney injury developed typically; the study simply tells us that, as a group, they deserve a closer watch. That distinction matters enormously for a worried parent, because a raised risk is something that careful follow-up and early support can help address.

What This Does — and Doesn't — Mean for Families

It is important to be clear about what this study shows. It found a connection, not a cause. Because babies with kidney injury tend to be sicker overall, some of the link may reflect the general seriousness of their illness rather than the kidney injury itself — and the researchers say so plainly [1]. Scientists have reasons to think the kidney and brain really do influence each other through inflammation [9], but this kind of study cannot settle whether treating the kidney would protect the brain.

If your baby had kidney injury in the NICU, the practical takeaway is reassuring rather than alarming: most babies recover kidney function, and this finding is a reason for attentive follow-up, not a prediction about your child. What it supports is making sure children who had kidney injury get careful developmental check-ups as they grow, so that any extra help — such as early therapy — can start as soon as it is useful. Doctors already know that early information about a baby's development, including brain scans in some cases, can help guide support [10]. Kidney injury simply adds one more reason to keep a close, caring eye on how a child is developing.

The History Behind This Moment

It is worth appreciating how new this way of thinking is. For a long time, a temporary rise in a baby's kidney blood test was noted and then largely set aside; the kidneys were assumed to bounce back with no lasting consequences, and attention went to the lungs, heart, and brain. Families of premature babies were rarely told anything about kidney health at all. Only in the last decade — after doctors agreed on how to define and measure newborn kidney injury and discovered how common it is [4],[5] — did it become possible to ask whether these early kidney events echo forward into childhood. This study is part of that shift, moving kidney injury from an overlooked lab value to a meaningful piece of a child's story.

What Researchers Are Working On Next

The next questions are the hopeful ones. Researchers want to know whether the two-year findings hold up as these children reach school age, and whether protecting the kidneys — by being careful with medications that can stress them and by keeping blood flow and fluids well balanced — can actually improve development. They also want to follow kidney health over time, because problems with kidney function later in childhood can affect growth and learning too [11]. Another open question is why the link showed up mainly in thinking-and-learning skills rather than in movement — a clue that researchers hope will eventually reveal exactly how an early kidney problem might touch the developing brain. Answering these questions will take years and larger studies that follow children well past their toddler check-ups, but each one moves the field closer to knowing whether protecting the kidneys can help protect a child's future. For now, the message from this research is simple and empowering: kidney injury in a very premature baby is common, usually recoverable, and a good reason for families and doctors to stay closely connected through the years of a child's development [1].

References

  1. Hanna M, Chock VY, Kamath N, Raj A, Swanson JR, Griffin R, Askenazi DJ, Nesargi S. Acute Kidney Injury and Neurodevelopmental Outcomes in Extremely Premature Neonates: A Secondary Analysis of a Randomized Clinical Trial. JAMA Netw Open. 2025;8(11):e2543270. doi:10.1001/jamanetworkopen.2025.43270 ↩
  2. Stoll BJ, Hansen NI, Bell EF, et al. Trends in care practices, morbidity, and mortality of extremely preterm neonates, 1993-2012. JAMA. 2015;314(10):1039-1051. doi:10.1001/jama.2015.10244 ↩
  3. Adams-Chapman I, Heyne RJ, DeMauro SB, et al. Neurodevelopmental impairment among extremely preterm infants in the Neonatal Research Network. Pediatrics. 2018;141(5):e20173091. doi:10.1542/peds.2017-3091 ↩
  4. Jetton JG, Boohaker LJ, Sethi SK, et al. Incidence and outcomes of neonatal acute kidney injury (AWAKEN): a multicentre, multinational, observational cohort study. Lancet Child Adolesc Health. 2017;1(3):184-194. doi:10.1016/S2352-4642(17)30069-X30069-X) ↩
  5. Askenazi DJ, Heagerty PJ, Schmicker RH, et al. Prevalence of acute kidney injury (AKI) in extremely low gestational age neonates (ELGAN). Pediatr Nephrol. 2020;35(9):1737-1748. doi:10.1007/s00467-020-04563-x ↩
  6. Al-Mouqdad MM, Jamjoom DZ, Abdalgader AT, et al. Association between acute kidney injury and brain injury on term-equivalent age brain magnetic resonance imaging in very preterm infants. Pediatr Nephrol. 2022;37(12):3235-3242. doi:10.1007/s00467-022-05534-0 ↩
  7. Chen CC, Chu CH, Lin YC, Huang CC. Neurodevelopment after neonatal acute kidney injury in very preterm-birth children. Kidney Int Rep. 2023;8(9):1784-1791. doi:10.1016/j.ekir.2023.06.020 ↩
  8. Juul SE, Comstock BA, Wadhawan R, et al. A randomized trial of erythropoietin for neuroprotection in preterm infants. N Engl J Med. 2020;382(3):233-243. doi:10.1056/NEJMoa1907423 ↩
  9. Yap SC, Lee HT. Acute kidney injury and extrarenal organ dysfunction: new concepts and experimental evidence. Anesthesiology. 2012;116(5):1139-1148. doi:10.1097/ALN.0b013e31824f951b ↩
  10. Woodward LJ, Anderson PJ, Austin NC, Howard K, Inder TE. Neonatal MRI to predict neurodevelopmental outcomes in preterm infants. N Engl J Med. 2006;355(7):685-694. doi:10.1056/NEJMoa053792 ↩
  11. Harshman LA, Johnson RJ, Matheson MB, et al. Academic achievement in children with chronic kidney disease: a report from the CKiD cohort. Pediatr Nephrol. 2019;34(4):689-696. doi:10.1007/s00467-018-4144-7 ↩