Keeping Very Premature Babies Warm With Plastic Wrap: How Were the Children Doing at Two?

A plain-language guide to Vincer et al. (BMC Pediatrics, 2026), which followed up babies from the Heat Loss Prevention trial to see whether wrapping at birth affected survival and development

Very premature babies lose heat fast after birth, so international experts suggest wrapping them in clear plastic in the first minutes of life. A follow-up of a large international trial found no clear difference in survival or development at about two years between wrapped and unwrapped babies. Many children could not be followed up, so the question is not fully settled, but wrapping remains a sensible way to keep babies warm.

If your baby was born very early, you may have seen a team place them in what looks like a clear plastic bag right after birth. It can look surprising, but it has a simple purpose: to stop a tiny body from cooling down. This article explains a new study that asked a question parents often wonder about, namely whether that warming step makes any difference to how children grow and develop over the following years [1].

Why keeping a tiny baby warm matters so much

Doctors have known for a long time that warmth and survival go together for premature babies. As far back as 1958, researchers were studying how the temperature around newborn premature babies affected whether they survived [2]. Later studies showed why newborns cool so quickly: the main way they lose heat in the first 15 to 30 minutes is through water evaporating from their wet skin, much as you feel cold stepping out of a swimming pool [3].

Babies born very early are especially at risk. A large study of 5697 babies born before 32 weeks of pregnancy across 19 regions in 11 European countries found that more than half (53.4%) arrived in the neonatal intensive care unit (NICU, the hospital ward for sick and premature newborns) with a temperature below 36.5 °C, which is lower than ideal [4]. Babies who arrive cold tend to do worse: in one large network study of 5277 small babies, each 1 °C drop in temperature on arrival went along with a 28% higher chance of dying [5]. But the researchers were careful to point out that being cold might be a sign that a baby was already sicker, rather than the cause of the problems [5].

In 1999 a team in Halifax tried something different from simply drying and warming: placing very premature babies, without drying them first, into a plastic wrap that holds in warmth and moisture. Babies born before 28 weeks who were wrapped arrived on the ward 1.9 °C warmer [6]. A second study in Hamilton confirmed this [7], a trial in Padua, Italy, found that babies who were only dried arrived colder than those given a plastic wrap or plastic cap [8], and later studies in places including Malaysia and India found the same warming effect [9][10]. When experts pulled all the studies together in 2018, they agreed that plastic wraps warm babies, but said there was not enough evidence to know whether wraps help babies survive, and they asked for studies of how children develop later [11].

How the study was done

To answer those bigger questions, doctors set up the Heat Loss Prevention (HeLP) trial, organised with the help of the Vermont Oxford Network in 39 hospitals across North America, Europe and Asia [1]. Between November 2004 and June 2010, babies born before 28 weeks were "randomised", which means a process like tossing a coin decided whether each baby would be wrapped in plastic or cared for without the wrap. This is the fairest way to compare two approaches, because chance, not anyone's choice, decides which babies get which care.

The first results, published in 2015, showed that wrapped babies were warmer but were no more likely to survive than unwrapped babies [12]. A small sister study of babies born before 24 weeks also found no difference in survival [13]. From the start, the researchers had planned to check on the children again at around two years of age [14].

The new paper reports that check-up [1]. Only 11 of the 39 hospitals had a formal follow-up clinic, where children born very early are routinely seen as they grow, so the study included the 356 babies born at those hospitals: 183 wrapped and 173 not wrapped. The children were seen at 18 to 24 months of "corrected age" (age counted from the mother's due date rather than the actual birth date, which gives premature babies a fairer comparison). They had a physical examination including a check of nerves and muscles, hearing and vision checks, and the Bayley test, a standard set of play-based tasks that measure early learning and development [1]. Because two different versions of the Bayley test were used over the years, the researchers used a published method to put the scores on the same scale [15].

The main thing the researchers counted was whether a child had died or had a developmental disability. A disability was defined as cerebral palsy (a condition affecting movement and muscle control), a low score on the Bayley test, blindness, or hearing loss needing hearing aids [1].

What the researchers found

The researchers knew how 240 of the 356 children were doing. In the wrapped group, 82 out of 113 children had died or had a disability, which is about 73 in every 100. In the unwrapped group, it was 80 out of 127, about 63 in every 100 [1].

At first glance, that looks worse for the wrap. But statistics, the tools scientists use to tell real differences from chance, showed that a gap this size could easily have happened by luck alone. When the researchers took into account other things that affect outcomes, such as birth weight and the mother's education, there was still no clear difference. And among the most premature babies, those born before 26 weeks, the pattern actually went the other way: about 76 in 100 wrapped babies had died or had a disability, compared with about 85 in 100 unwrapped babies, again a difference that could be due to chance [1].

Among the children who survived, the rates of cerebral palsy, low development scores, deafness and blindness were not significantly different between the groups. For example, 5 of 70 wrapped children and 6 of 87 unwrapped children had hearing loss needing aids. As in the original trial, wrapped babies were warmer when they arrived in the NICU, and there was a slightly higher chance of becoming too warm [1].

Why the results are less clear than they first look

The biggest problem was that about one in three children (116 of 356) could not be followed up, and this happened more often in the wrapped group (38 in 100) than the unwrapped group (27 in 100) [1]. The children who were missed tended to be bigger and born a little later, which usually means they were at lower risk. So the wrapped children who were checked may have been, on average, a slightly higher-risk group, and that alone could tip the numbers.

The study was also small for a question this important. The researchers calculated that it had only a 40% chance of detecting even a large benefit, cutting death or disability by half [1]. A study this size cannot prove that the wrap causes harm, and it cannot prove that the wrap has no effect at all. The children were also born many years ago, and the researchers note that the results apply mainly to hospitals in wealthier countries [1].

What this means for your baby

If your baby was wrapped at birth, this study does not show that wrapping harmed children. The wrap did what it was designed to do, keeping babies warmer when they arrived in the NICU, and there was no clear difference in how children were doing at two. The authors concluded that the wrap remains a simple and inexpensive way to prevent babies from getting too cold [1].

Today, international experts suggest that very premature babies be protected from cold with a warm delivery room, a radiant warmer, a plastic bag or wrap and a hat, while staff watch carefully that babies do not overheat [16]. Your baby's team checks temperature closely for this reason. You are always welcome to ask what temperature your baby had on arrival in the NICU and how it is being watched.

Perhaps the most useful message for families is about follow-up visits. This study struggled because many children were never seen again. Attending your baby's developmental check-ups helps your own child, because any difficulties can be spotted and supported early, and it helps researchers learn what really works for babies in the future.

What researchers are working on next

The authors think a trial as large as HeLP is unlikely to be repeated [1]. Instead, research is moving towards "bundles" of warming steps used together. An analysis combining many studies found early signs that adding a plastic hat, or warmed and moistened breathing gases, to the wrap might bring extra benefits, although the evidence is not yet strong [17]. Researchers are also keen to bring these simple measures to countries where many more babies get cold after birth; in East Africa, for example, more than half of newborns studied had low temperatures [18]. You can read about one such effort in our article on a warm-chain programme in rural Ethiopia.

The bottom line

Wrapping very premature babies in plastic at birth keeps them warmer. The only long-term study of this practice found no clear difference in survival or development at about two years, but it was too small, and lost too many children along the way, to give a final answer. For now, the wrap remains a sensible part of keeping the smallest babies warm, together with careful temperature checks and regular follow-up as children grow.

References

  1. Vincer MJ, Reilly MC, Vohra S, et al. Randomized trial of occlusive wrap for heat loss prevention in preterm infants: neurodevelopmental outcome. BMC Pediatr. 2026;26(1):781. doi:10.1186/s12887-025-05678-6 ↩
  2. Silverman WA, Fertig JW, Berger AP. THE INFLUENCE OF THE THERMAL ENVIRONMENT UPON THE SURVIVAL OF NEWLY BORN PREMATURE INFANTS. Pediatrics. 1958;22(5):876-886. doi:10.1542/peds.22.5.876 ↩
  3. Hammarlund K, Nilsson GE, Oberg PA, Sedin G. Transepidermal water loss in newborn infants. V. Evaporation from the skin and heat exchange during the first hours of life. Acta Paediatr Scand. 1980;69(3):385-392. doi:10.1111/j.1651-2227.1980.tb07097.x ↩
  4. Wilson E, Maier RF, Norman M, et al. Admission Hypothermia in Very Preterm Infants and Neonatal Mortality and Morbidity. J Pediatr. 2016;175:61-67.e4. doi:10.1016/j.jpeds.2016.04.016 ↩
  5. Laptook AR, Salhab W, Bhaskar B. Admission temperature of low birth weight infants: predictors and associated morbidities. Pediatrics. 2007;119(3):e643-649. doi:10.1542/peds.2006-0943 ↩
  6. Vohra S, Frent G, Campbell V, Abbott M, Whyte R. Effect of polyethylene occlusive skin wrapping on heat loss in very low birth weight infants at delivery: a randomized trial. J Pediatr. 1999;134(5):547-551. doi:10.1016/S0022-3476(99)70238-670238-6) ↩
  7. Vohra S, Roberts RS, Zhang B, Janes M, Schmidt B. Heat Loss Prevention (HeLP) in the delivery room: A randomized controlled trial of polyethylene occlusive skin wrapping in very preterm infants. J Pediatr. 2004;145(6):750-753. doi:10.1016/j.jpeds.2004.07.036 ↩
  8. Trevisanuto D, Doglioni N, Cavallin F, Parotto M, Micaglio M, Zanardo V. Heat loss prevention in very preterm infants in delivery rooms: a prospective, randomized, controlled trial of polyethylene caps. J Pediatr. 2010;156(6):914-917.e1. doi:10.1016/j.jpeds.2009.12.021 ↩
  9. Rohana J, Khairina W, Boo NY, Shareena I. Reducing hypothermia in preterm infants with polyethylene wrap. Pediatr Int. 2011;53(4):468-474. doi:10.1111/j.1442-200X.2010.03295.x ↩
  10. Nimbalkar SM, Khanna AK, Patel DV, Nimbalkar AS, Phatak AG. Efficacy of Polyethylene Skin Wrapping in Preventing Hypothermia in Preterm Neonates (<34 Weeks): A Parallel Group Non-blinded Randomized Control Trial. J Trop Pediatr. 2019;65(2):122-129. doi:10.1093/tropej/fmy025 ↩
  11. McCall EM, Alderdice F, Halliday HL, Vohra S, Johnston L. Interventions to prevent hypothermia at birth in preterm and/or low birth weight infants. Cochrane Database Syst Rev. 2018;2(2):CD004210. doi:10.1002/14651858.CD004210.pub5 ↩
  12. Reilly MC, Vohra S, Rac VE, et al. Randomized trial of occlusive wrap for heat loss prevention in preterm infants. J Pediatr. 2015;166(2):262-8.e2. doi:10.1016/j.jpeds.2014.09.068 ↩
  13. Reilly MC, Vohra S, Rac VE, et al. Parallel Exploratory RCT of Polyethylene Wrap for Heat Loss Prevention in Infants Born at Less than 24 Weeks' Gestation. Neonatology. 2019;116(1):37-41. doi:10.1159/000497253 ↩
  14. Vohra S, Reilly M, Rac VE, et al. Study protocol for multicentre randomized controlled trial of HeLP (Heat Loss Prevention) in the delivery room. Contemp Clin Trials. 2013;36(1):54-60. doi:10.1016/j.cct.2013.06.001 ↩
  15. Moore T, Johnson S, Haider S, Hennessy E, Marlow N. Relationship between test scores using the second and third editions of the Bayley Scales in extremely preterm children. J Pediatr. 2012;160(4):553-558. doi:10.1016/j.jpeds.2011.09.047 ↩
  16. Ramaswamy VV, Dawson JA, de Almeida MF, et al. Maintaining normothermia immediately after birth in preterm infants <34 weeks' gestation: A systematic review and meta-analysis. Resuscitation. 2023;191:109934. doi:10.1016/j.resuscitation.2023.109934 ↩
  17. Abiramalatha T, Ramaswamy VV, Bandyopadhyay T, et al. Delivery Room Interventions for Hypothermia in Preterm Neonates: A Systematic Review and Network Meta-analysis. JAMA Pediatr. 2021;175(9):e210775. doi:10.1001/jamapediatrics.2021.0775 ↩
  18. Beletew B, Mengesha A, Wudu M, Abate M. Prevalence of neonatal hypothermia and its associated factors in East Africa: a systematic review and meta-analysis. BMC Pediatr. 2020;20(1):148. doi:10.1186/s12887-020-02024-w ↩