Keeping the Tiniest Babies Warm: Does It Matter Where the Temperature Sticker Goes?

A plain-language look at a randomized trial (Jani et al., Pediatric Research 2024) on temperature-probe placement for very premature newborns

Keeping a very premature baby warm in the first minutes after birth is one of the most important — and surprisingly difficult — jobs in the delivery room, because these tiny infants lose heat extraordinarily fast. A team of doctors and nurses in Sydney, Australia ran a careful experiment to see whether one small detail makes a difference: whether the little temperature sensor that guides the warming bed is taped to a baby's upper back or under the arm. They found that the upper back worked at least as well as the underarm spot, kept slightly more babies at a healthy temperature, and appeared to help the smallest babies the most — all without any downside.

Why staying warm is such a big deal

A baby born many weeks early arrives wet, with paper-thin skin and almost none of the body fat that older babies and adults use to hold in heat. Left alone even briefly, such a baby can become cold very quickly, and being cold at this stage is genuinely dangerous — not just uncomfortable. Doctors describe a healthy body temperature as "normothermia," roughly 36.5 to 37.5 degrees Celsius. When premature babies arrive at the neonatal intensive care unit (NICU) colder than that, they are more likely to face serious problems.

This is not a vague worry; it is one of the most consistent findings in newborn medicine. Large studies have shown that premature babies who are cold when they arrive in the NICU have a higher chance of dying [1], a higher risk of death or lasting problems with brain development [2], and more complications such as a serious bowel illness [3]. Because the danger is so clear, keeping newborns warm has become a top priority that hospitals measure and track closely.

How doctors learned to fight the cold — and what was still missing

Over the past two decades, delivery-room teams have assembled a whole toolkit to trap heat, and they use these tools together as a routine "bundle." A large review of the research confirms that these measures reduce cold-related problems, though they don't erase them entirely [4]. Some of the key steps were proven in their own experiments: wrapping babies in clear plastic instead of drying them [5], and, in places with fewer resources, slipping newborns into simple food-grade plastic bags [6]. The hospital that ran this study had already built a careful warming routine of its own, and yet a stubborn handful of babies still ended up cold [7]. That leftover problem is what pushed the team to look at the small stuff the routine never spelled out.

One of those overlooked details is where to place the temperature sensor. Modern warming beds work automatically: a small probe taped to the baby's skin constantly reports the temperature, and the bed raises or lowers its heat to hold the baby near 37 degrees. In other words, that one sensor is quietly steering the whole system — so where it sits could actually matter. When researchers surveyed hospitals around the world, they discovered there was no agreement at all on the best spot [8]. An earlier experiment had compared a few sensor positions but only in somewhat larger premature babies, and found them roughly equal [9], while a review of the topic concluded that the question was genuinely unsettled and deserved a proper study that included the very smallest infants [10].

What the researchers did

To answer the question fairly, the team ran what is called a randomized trial — the gold standard for comparing two approaches, in which a computer, not a doctor's preference, decides which option each baby gets, so the two groups end up well matched [11]. The study took place at Westmead Hospital, a large specialist maternity centre in Sydney, Australia. Babies born very early — between about 23 and 32 weeks of pregnancy (a full-term pregnancy is around 40 weeks) — were randomly assigned to have the temperature sensor placed either on the left upper back or under the left arm.

The important thing is that everything else was kept exactly the same for both groups. Every baby got the identical warming routine: the automatic heated bed set to 37 degrees, an immediate plastic wrap, a lined bonnet to cover the head, delayed cutting of the umbilical cord for at least a minute, and warmed, moist air for breathing support. The only difference between the two groups was the spot where the sensor was taped. The researchers then measured each baby's temperature the moment they arrived in the NICU, a trip that took about 10 to 15 minutes from the delivery room. In all, 178 babies took part and 175 were included in the final results.

What they found

More of the babies with the sensor on the upper back arrived at a healthy temperature. Using the hospital's strict target range, about 45 out of every 100 upper-back babies were in the ideal range, compared with about 32 out of every 100 underarm babies. Using the slightly wider healthy range, the figures were about 90 out of 100 versus 80 out of 100. These differences pointed clearly in the same direction, but they were small enough that they could have happened by chance, so the researchers were careful not to overclaim. What gives the finding weight is that every single measurement leaned the same way: the upper-back babies had a higher average temperature, and fewer of them became genuinely cold (about 9 in 100 versus 19 in 100).

The most eye-catching result was in the tiniest, most fragile babies — those born before about 28 weeks. In this group the upper-back position made a much bigger difference, enough that roughly one extra baby out of every three benefited. Just as importantly, the upper-back spot caused no problems: virtually no baby became too hot, none developed any skin irritation from the sensor, and the rates of other newborn complications were the same whether the sensor was on the back or under the arm. In short, the new position was at least as safe and possibly a little better.

What this means for families

If your baby is cared for in a NICU that uses one of these automatic warming beds, this study is quietly reassuring. It shows that the team has good reason to place the temperature sensor on the upper back, a spot that is easy to reach, sits on flat skin, is less likely to be knocked loose during the flurry of activity right after birth, and may help hold in warmth — especially for the smallest babies. It is a change that costs nothing, adds no risk, and could give the most vulnerable newborns a slightly warmer, safer start. For parents, the sensor's position is not something you will see or feel any difference from; what it reflects is a team paying attention to the small details that add up to good care.

Why might the back be the better spot? The researchers offer a few simple reasons. The upper back is flat, so the sensor can lie flush against the skin and read the temperature accurately, whereas the underarm area is more uneven and tucked away. The back is also less likely to be bumped or peeled loose during the busy, hands-on work of helping a new baby breathe and settle. And because a sensor that loses contact tends to under-read — telling the warming bed the baby is cooler than she really is — a well-placed sensor helps the automatic bed deliver just the right amount of heat, no more and no less. None of this was proven directly by the study, but it is a sensible explanation for why the numbers leaned the way they did.

It is also fair to be honest about the study's limits, as the researchers were. It was done at a single hospital, everyone knew which spot was being used (it cannot be hidden), and the results apply to units using this particular type of warming bed and routine — not necessarily to every hospital everywhere. The researchers even noted that simply running the study may have made staff extra attentive, which could have made the underarm group look better than usual and narrowed the gap. These are reasons to see the finding as promising rather than final, and this is exactly why experts describe keeping babies warm as the result of many small steps working together rather than any single trick [12].

What researchers are working on next

Because a single study of 175 babies can only take the question so far, the team designed their trial to feed into a larger worldwide analysis that will pool results from similar studies, which should give a much clearer answer about whether the upper back truly is the better spot. The researchers also point out that low-risk comparisons like this one — where both choices are already normal, safe care — might in future be studied using simpler consent approaches, so that more families can take part and the answers apply to more babies [13]. For now, the message is small but encouraging: a piece of tape in the right place may be one more quiet way to keep the tiniest newborns warm.

References

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  2. Ting JY, Synnes AR, Lee SK, Shah PS. Association of admission temperature and death or adverse neurodevelopmental outcomes in extremely low-gestational-age neonates. J Perinatol. 2018;38(7):844–849. doi:10.1038/s41372-018-0099-6 ↩
  3. Tay VY, et al. Admission temperature and hospital outcomes in extremely preterm infants. J Paediatr Child Health. 2019;55(2):216–223. doi:10.1111/jpc.14187 ↩
  4. 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 ↩
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  6. Leadford AE, et al. Plastic bags for prevention of hypothermia in preterm and low birth weight infants. Pediatrics. 2013;132(1):e128–e134. doi:10.1542/peds.2012-2030 ↩
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  8. Jani P, et al. Thermoregulation and golden hour practices in extremely preterm infants: an international survey. Pediatr Res. 2023;93(6):1701–1709. doi:10.1038/s41390-022-02297-0 ↩
  9. Bensouda B, et al. Temperature probe placement during preterm infant resuscitation: a randomised trial. Neonatology. 2018;113(1):27–32. doi:10.1159/000480537 ↩
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