When a Newborn Isn't Getting Enough Milk: Understanding High-Sodium Dehydration

What three recent studies from Colombia, India and Türkiye tell families about which babies are at risk, why early checks matter and how doctors correct the problem gently

A small number of newborns do not get enough milk in their first days, lose too much water and end up with too much salt (sodium) in their blood. Three recent studies show which babies are most at risk, how serious this can become when it is noticed late, and how doctors can bring the salt level down gently. Breastfeeding is not the problem; unnoticed low milk intake is, and simple checks can help catch it early.

Why the first days of feeding matter so much

In the first days after birth, a baby and a mother are both learning to breastfeed, and it can take time before milk flows well and the baby feeds effectively. Almost all babies lose a little weight during this time, which is normal. Occasionally, though, a baby takes in too little milk for too long. The baby then loses more water than expected, and the salt in the blood becomes concentrated, a condition doctors call hypernatremic dehydration ("hyper" meaning too much, "natremia" referring to sodium). It is uncommon, and when it is spotted early it is usually treated successfully.

Three recent studies look at this problem from different angles. A team at Universidad de La Sabana in Colombia gathered and combined earlier studies of healthy, full-term, breastfed babies to work out how often the condition happens and which babies are most at risk [1]. A team at a large hospital in Indore, India, followed 60 babies admitted to its neonatal intensive care unit (NICU), the hospital ward for newborns who need special care; most of those babies were born early or small, were fed formula or other milks, and arrived with diarrhea a few weeks after birth [2]. A team at Dokuz Eylül University Hospital in İzmir, Türkiye, looked back over ten years of records to see which kind of drip fluid (fluid given through a vein) brought the sodium down most safely in full-term babies [3]. All three studies point to the same root cause, too little fluid going in, but they describe quite different groups of babies.

How doctors first came to recognize this problem

Breastfeeding brings well-established benefits for babies and mothers, and health organizations recommend it strongly [4], [5]. That is one reason doctors were careful when, in the late 1990s and early 2000s, reports began to describe breastfed babies who became dehydrated. In northern England, researchers found 8 affected babies among about 32,000 births in one year, or at least 2.5 babies in every 10,000; in every case the only explanation was that breastfeeding had not become established successfully [6]. In Pittsburgh in the United States, doctors reviewing five years of hospital admissions found that 9 in 10 affected babies had gone home within two days of birth, most mothers were having their first baby, and yellowing of the skin (jaundice) was the most common sign that brought them back [7]. Because families were now going home earlier, the key days for spotting feeding difficulties were increasingly spent at home rather than on the maternity ward.

Doctors in Ankara, Türkiye, then showed that babies found early, around day three, had much lower sodium levels than babies described in older reports who were found closer to two weeks of age [8]. A study in Iran that followed affected babies for two years found that some had developmental delays, which became less common as the children grew, and that delays were more likely when the sodium had been very high [9]. Meanwhile, a review of treatment studies found no firm agreement on how quickly doctors should bring sodium down, only a sign that going slowly seemed safer [10]. These gaps are what the three new studies set out to fill.

Three studies, three pieces of the puzzle

The Colombian study is a "systematic review and meta-analysis", meaning the team searched five research databases, selected the 13 studies that met strict standards and combined their results to get a clearer overall picture [1]. The Indian study was "prospective": the team decided in advance what to measure and then recorded it for every eligible baby over one year [2]. The Turkish study was "retrospective", looking back at the medical records of 138 babies who needed a drip, and comparing three fluids that contain different amounts of salt [3]. Each design has strengths and limits, which is why the studies are most useful when read together.

Which babies are most likely to be affected

Across ten studies, about 1.4 in every 100 full-term, fully breastfed babies developed the condition, although the individual studies disagreed widely, so this is only a rough guide [1]. Some patterns were clearer. Babies were more likely to be affected when the first breastfeed was delayed (about six times higher odds), when they passed urine fewer than six times a day (about eight times higher odds), when their mother was having her first baby, and when they were born after 40 weeks of pregnancy. Losing more than 10% of birth weight was also linked to the problem, although that particular number could not be measured precisely. One of the combined studies found that affected babies came back to hospital between days two and five, without a timely weight check or support at home, and across the studies the most common reasons for coming back were fever, unusual sleepiness and jaundice [1]. One study from India found that a simple score of how well a baby latches onto the breast was much lower in affected babies [11].

It helps to know what normal looks like. In one large study of babies in California, half of those born vaginally were back to their birth weight by day nine [12], and a study of more than 1,000 babies in Iran found an average loss of about 4% of birth weight at three to five days [13]. Weight loss is expected; it is losing more than expected, or not starting to regain, that deserves a closer look. That is why nurses, midwives and doctors weigh babies in the first days and compare the result with what is typical for a baby of the same age.

What happens when the problem is found late

The Indian study shows what can happen when dehydration is recognized late in a group of babies who are already vulnerable. More than half were born early, more than eight in ten were small at birth, and most (51 of 60) were fed formula, animal milk or a mix rather than breast milk alone [2]. Most arrived in the second to fourth week of life, often with loose stools and refusing feeds. These babies were very unwell: more than a third had kidney injury, and a few had bleeding in the brain or a clot in the brain's veins, problems that doctors look for carefully in any baby with very high sodium. Sadly, 17 of the 60 babies died, and deaths were more common when the sodium was highest. These babies are quite different from the healthy, full-term breastfed babies in the other two studies, but the lesson is shared: the earlier a feeding problem is noticed, the better.

How doctors bring the sodium level down safely

When a baby needs a drip, doctors try to bring the sodium down slowly, because earlier research suggested that a gentle, gradual correction is safer [10]. The Turkish study compared three drip fluids: one with a normal amount of salt (called 0.9% saline) and two with less salt [3]. The lower-salt fluids brought the sodium down faster. With the lowest-salt fluid, 17 of 40 babies (about four in ten) had a fall faster than the recommended speed, compared with 3 of 44 (about one in fifteen) with normal saline. Reassuringly, no difference in complications or deaths was seen between the groups. The limits the authors cite are a fall of less than 0.5 units (mmol/L) per hour and less than 12 units per day, and they concluded that normal saline appears to be the more suitable choice. A larger Turkish study of routine drip fluids in 420 full-term newborns across 21 hospitals, called the "neofluid" study, also linked lower-salt fluids to more cases of sodium dropping too low [14]. The İzmir team is careful to say their study was small and that doctors, not chance, decided which fluid each baby received, so a fairer comparison is still needed.

What this means for families

The most important message is that breastfeeding itself is not the cause; the problem is milk not getting to the baby while feeding is still being established, and the study authors call for early feeding assessment and support for mothers [1]. The studies point to a few things families can notice: how many wet diapers the baby has, whether the baby is feeding well and seems satisfied, whether the baby is unusually sleepy or hard to wake, whether the skin or eyes are turning yellow, and whether the baby has a fever. Weight checks in the first days, including a check a few days after going home, are a routine and valuable part of care. If anything about feeding, wet diapers or your baby's alertness worries you, contact your midwife, nurse, lactation consultant or doctor promptly; they would always rather check. Jaundice often appears alongside feeding difficulties, and the In[Neo]Sight article on phototherapy for newborn jaundice explains how it is treated.

What researchers are working on next

The study teams are calling for a single agreed definition of the condition so that studies can be compared fairly [1], for tests of whether a routine check two to three days after going home prevents serious cases [1], and for a properly randomized trial comparing drip fluids in babies with different sodium levels [3]. Together, these three studies suggest that high-sodium dehydration can often be prevented or caught early through attentive feeding support and simple checks, and that when a drip is needed, doctors are learning how to correct it gently and safely.

References

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