When a Premature Baby's Kidneys Stop Working

What three recent reports on dialysis in newborns — from Rome, Belgrade and eastern China — tell families about a difficult decision

When a premature baby's kidneys stop working, doctors can take over that job with dialysis — but there is very little evidence about when to start or which method to use. Three reports published between 2025 and 2026 show what happens in practice: two found that most babies treated after several days without urine still died, while a third described a very small baby who recovered completely after treatment began within a day of birth.

Why the kidneys matter so much in a sick newborn

The kidneys do more than make urine. They control how much fluid stays in the body, keep salts such as potassium and sodium in a narrow safe range, remove waste products that build up from normal metabolism, and help regulate the acidity of the blood. A newborn baby — especially one born many weeks early — has kidneys that are still under construction. The filtering units are immature, the blood vessels supplying them are narrow and easily squeezed shut, and the whole system depends heavily on steady blood pressure and a good oxygen supply. A period of low blood pressure, a serious infection, or a difficult birth with a lack of oxygen can shut those kidneys down quickly.

When that happens, the medical term is acute kidney injury. In neonatal intensive care it is common rather than exotic, and a large international study involving many hospitals confirmed that babies who develop it are more likely to die and to stay in hospital longer than babies who do not [1]. Doctors now have agreed criteria for recognising it, based on the amount of urine a baby passes and on a blood test called creatinine [2], [3].

How families and doctors have faced this problem in the past

For decades the situation was this: everyone could agree on the diagnosis, and nobody could agree on the treatment. If medicines to support blood pressure and encourage urine production failed, the remaining option was dialysis — using an artificial process to do the kidneys' work.

The older of the two main methods is called peritoneal dialysis. A soft tube is placed into the abdomen, a small volume of sterile fluid is run in, left to sit for fifteen or twenty minutes, and then drained out, carrying waste and excess water with it. It needs no connection to a blood vessel and no blood-thinning medication, which is why international guidance has long recommended it as a reasonable first choice in the smallest babies [4]. The difficulty is that no manufacturer makes a dialysis tube designed for a baby weighing under a kilogram. Doctors have improvised for years with intravenous cannulas, drainage tubes and catheters intended for other purposes, and the published reports describe leaking, blockages, infection of the abdominal lining, and a great many deaths [5], [6], [7].

The newer method is called continuous renal replacement therapy. Here blood is drawn out through a small tube in a large vein, passed slowly through a filter, and returned. It removes fluid more precisely and more gently, which suits a baby whose circulation is fragile. It was borrowed from intensive care for older children, where studies showed it could be done in patients weighing ten kilograms or less but that results got worse the smaller the child was [8], [9]. In 2014 a team in Italy built the first machine designed specifically for newborns and used it in a baby [10]. More than a decade later, most hospitals still adapt adult equipment, and which method a baby receives depends heavily on which hospital they are in [11].

What the three new reports describe

The first report comes from a large neonatal unit in Rome [12]. Between 2021 and 2025, twelve premature babies there received peritoneal dialysis after every available medicine had failed. Most had been born extremely early — the middle of the group was around 28 weeks — and their underlying problems varied: infection with shock in four, severe fluid build-up before birth in three, complications of a shared twin pregnancy in two, and single cases of oxygen deprivation at birth, bowel inflammation and an abnormal heart rhythm. Only two of the twelve were still passing any urine when dialysis started. The others had passed none for between two and six days.

Two babies recovered kidney function. Eleven of the twelve died. Half of those deaths were caused by infection and half by the underlying illness spreading to other organs. The Rome team also gathered every similar report ever published — ninety-two premature babies in twenty papers — and found that just over half had died and about a third had survived or recovered kidney function. They are careful to say that twelve babies cannot prove anything, and that what is missing from the whole literature is a consistent record of how long each baby had gone without urine before dialysis was started.

The second report comes from the University Children's Hospital in Belgrade and covers ten years [13]. Forty-one newborns, all transferred in from other hospitals, received continuous filtering therapy. They were bigger and more mature than the Rome group — most were around 35 weeks and about 2.3 kilograms — and thirty-one died. What is useful here is which things predicted the outcome and which did not. How early the baby was born, how much they weighed, and how sick they scored on admission did not separate those who lived from those who died. What did: whether the baby started making urine again during treatment. All nineteen babies who made none died. Complications during treatment mattered too — bleeding, unstable blood pressure or problems with the filter circuit — and those affected were far more likely to die than the eight babies who had none.

The third report is a single baby in eastern China, and it reads very differently [14]. She was the smaller of identical twins who shared a placenta unequally, born at almost 32 weeks weighing 1,470 grams, and she arrived in very poor condition — cold, barely responsive, with dangerously acidic blood. In nine hours she passed about two millilitres of urine. Instead of waiting for fluid to build up, her team started continuous filtering therapy twenty hours after she was born, beginning at the gentlest possible settings and increasing them only once she proved she could tolerate it. Thirty-seven hours later they stopped. Her urine output had recovered, her blood chemistry had normalised, and she went home on day 35. At six months her kidneys were working normally and her growth and development were on track. Her twin sister, who had not been deprived of oxygen, never developed the problem at all.

What these reports do and do not mean

It is tempting to conclude that the newer method works and the older one does not. That is not what the evidence shows, and it is worth being clear about why. The babies in Rome were treated after days without urine, when several organs were already failing; the babies in Belgrade who died quickly died of the illness that damaged their kidneys, not of the treatment; and the baby in China had one severe but potentially reversible injury and was, at 1,470 grams, at the larger end of the very small. Comparing them directly is like comparing three rescue attempts made at three different points in a fall.

What the reports genuinely agree on is more modest and more useful. Waiting is not neutral: fluid that accumulates while the kidneys are failing is itself harmful, and this has been shown repeatedly in critically ill children [15]. And the single most informative sign at the bedside is whether a baby begins to pass urine again once treatment starts. In both cohorts, babies who did not were the babies who did not survive.

What this means for families

If your baby is facing this decision, a few things are worth knowing. Honest survival figures across all three reports and the older literature they gather are sobering — closer to one in three than one in two — and any team that gives you a confident number is overstating what is known. Much of that outcome is determined by the illness that damaged the kidneys, not by the machine used to support them. Both methods are legitimate; a team choosing peritoneal dialysis over blood filtering is usually reflecting your baby's blood pressure, size and abdominal anatomy rather than a preference for one technology.

It is entirely reasonable to ask three specific questions: how long has my baby gone without urine, what would make you start today rather than tomorrow, and what will you be watching for to tell whether this is working? Those are the questions the clinicians themselves are wrestling with, and asking them is not second-guessing the team — it is joining a conversation they are already having.

What researchers are working on next

The clearest unfinished task is deciding when to begin. Every one of these reports ends by saying that no one has ever tested a starting threshold in newborns, and the Rome authors name establishing that threshold as their central recommendation. A second effort concerns earlier detection: creatinine, the standard blood test, rises only after considerable damage has been done, and in a newborn's first days it partly reflects the mother's levels rather than the baby's. Researchers are testing urine markers that signal kidney injury sooner, a subject In[Neo]Sight has covered separately in its article on an early urinary marker of newborn kidney injury. Third, purpose-built newborn dialysis machines exist but remain rare, and until they are widely available technique will keep varying between hospitals. Finally, several groups are arguing for a shared international register so that the one number nobody currently records consistently — the hours between a baby stopping passing urine and treatment beginning — is finally measured.

References

  1. 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;1:184–194. doi:10.1016/S2352-4642(17)30069-X30069-X) ↩
  2. Selewski DT, Charlton JR, Jetton JG, et al. Neonatal acute kidney injury. Pediatrics. 2015;136:e463–e473. doi:10.1542/peds.2014-3819 ↩
  3. Coleman C, Tambay Perez A, Selewski DT, Steflik HJ. Neonatal Acute Kidney Injury. Front Pediatr. 2022;10:842544. doi:10.3389/fped.2022.842544 ↩
  4. Nourse P, Cullis B, Finkelstein F, et al. ISPD guidelines for peritoneal dialysis in acute kidney injury: 2020 Update (paediatrics). Perit Dial Int. 2021;41:139–157. doi:10.1177/0896860820982120 ↩
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  7. Yu JE, Park MS, Pai KS. Acute peritoneal dialysis in very low birth weight neonates using a vascular catheter. Pediatr Nephrol. 2010;25:367–371. doi:10.1007/s00467-009-1347-y ↩
  8. Askenazi DJ, Goldstein SL, Koralkar R, et al. Continuous renal replacement therapy for children ≤10 kg: a report from the Prospective Pediatric Continuous Renal Replacement Therapy Registry. J Pediatr. 2013;162:587–592.e3. doi:10.1016/j.jpeds.2012.08.044 ↩
  9. Sanderson KR, Warady B, Carey W, et al. Mortality Risk Factors among Infants Receiving Dialysis in the Neonatal Intensive Care Unit. J Pediatr. 2022;242:159–165. doi:10.1016/j.jpeds.2021.11.025 ↩
  10. Ronco C, Garzotto F, Brendolan A, et al. Continuous renal replacement therapy in neonates and small infants: development and first-in-human use of a miniaturised machine (CARPEDIEM). Lancet. 2014;383:1807–1813. doi:10.1016/S0140-6736(14)60799-660799-6) ↩
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  12. Riitano F, Ferretti S, Costa S, Tiberi E, Gatto A, Vento G. Acute Peritoneal Dialysis in Critical Preterm Infants: A Case Series and Review of the Literature. Children (Basel). 2025;12(9):1113. doi:10.3390/children12091113 ↩
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  15. Sutherland SM, Zappitelli M, Alexander SR, et al. Fluid overload and mortality in children receiving continuous renal replacement therapy: the Prospective Pediatric Continuous Renal Replacement Therapy Registry. Am J Kidney Dis. 2010;55:316–325. doi:10.1053/j.ajkd.2009.10.048 ↩