The Significance of Blood Sugar Measurements in Newborns
I had this fabulously scarring episode when I was a second-year resident, post
-call from a crazy-busy night in the Pediatric Intensive Care Unit, where I
mentioned during rounds that a patient’s white blood cell count was 13.5 (yes, I
still remember that number). My attending stopped me, mid-sentence, and wrote 13.5 on a
piece of paper and threw it into the air. I watched its flight with a
sense of trepidation. This would not be good. As it landed at my
feet, my beloved attending
said “Jenny, what’s that?” I dutifully replied, “It’s this child’s white
blood cell count.” He then uttered words that have stuck with me forever:
“No, it’s a random number flying through the air."
Since that day, and because of that thought-changing episode, I get very
frustrated when I hear numbers given out of context, especially when we act on
numbers just because they are numbers. Those numbers should help complete
a picture, and that picture should start with a good look at the baby. The
number should not start the process- it should enhance it. And if the number is
not going to help, we do not need it.
concept that numbers need to contribute something to the care of the infant in a
meaningful way is the theme behind my three B's:
bilirubin, birth weight and blood sugar.
"Blood sugar" is the concentration of glucose in the blood. No
other types of sugar are measured. To understand the significance of any blood
glucose number in a neonate, we need to understand normal glucose metabolism in
the brand newborn.
a healthy full term infant, the blood glucose concentration decreases because
the flow of nutrition
the baby was receiving stops with the delivery of the placenta. Normally,
is the main source of energy for the brain.
But while mom's metabolism gets ready for lactation immediately after birth,
with no placenta to provide nutrients, and before the baby starts suckling,
glucose is scarce. This means the baby goes through a period of low blood
sugar. This is normal and expected.
baby compensates for the scarcity of glucose by using other fuels to keep the
brain happy. These fuels are things like ketone bodies, lactate and pyruvate. If
those fuels sound familiar to you, it's likely that you had to learn something
about the Kreb's cycle somewhere in your education. (And that means you're
groaning a little now!) The Kreb's cycle produces energy that can be used
throughout the body. These other fuels work together to make sure
that the newborn brain does not suffer injury.
When we are checking babies to make sure their blood glucose is acceptable, we
are doing so to prevent brain injury. However, since we only measure blood
glucose and not the amount of ketone bodies, pyruvate or lactate, we get a
number. A number that tells us glucose levels but doesn’t measure alternative
sources of energy: a random number
flying through the air.
let’s say have new term baby with a measured glucose of 28.
Does that baby have symptoms? Kids without
symptoms are doing something right. We do not need to intervene because
our exam told us the baby looked good. The number did not add to our
management and therefore we did not need it. That
glucose of 28 may mean nothing if the baby makes up for it with creation of
alternative fuels (which they do normally). Kids with no symptoms from their low blood sugar
(however we define it) do not need to be treated. Our next step is to do what we should be doing
already: skin-to-skin snuggling, feeding within an hour after birth,
and frequent breastfeeding with rooming-in.
When we treat an asymptomatic child with a "low" blood sugar (again,
however it is defined) with something other than
breastmilk, the production of alternative fuels gets messed up. The baby
needed a low blood glucose to start the pathways that create alternative fuel production. When we
give formula or glucose water, we are giving glucose, and those other pathways
that created ketone bodies, pyruvate and lactate as compensation for the low
blood sugar are now not needed. Those other newborn pathways may be delayed in working
or just stop. Because we messed with normal physiology, and may have
interrupted alternate fuel production, the babies may need continued
supplementation to maintain normal blood glucose.
The production of alternative fuels does not just work to meet the energy needs
of the brain. Ketone bodies are also used in brain myelination (nerve growth)
and the creation of lung surfactant (lung function). That means that the
normal dip in blood glucose, which creates other fuels, leads to brain energy,
nerve growth and lung development. We want that to occur without
interruption. We should not supplement a normal, term, asymptomatic baby
with low blood glucose.
baby with a low blood sugar and
symptoms, well, that’s a
problem. Symptomatic blood sugar can show up as irritability,
seizures, lethargy, turning blue, coma, not being able to maintain your
temperature, irregular breathing, among other evil things. Now look at
that list and see if we want to chalk any or one of those symptoms up to just a
low blood sugar. That baby could be sick. Really sick. Like
"take them to the ICU sick."
What’s up with that baby that they didn’t compensate for their low glucose with
those ketone bodies? What went wrong? Maybe the baby is premature, or
late-preterm and can’t
create ketone bodies or alternative body fuel because their liver is not mature
enough. Maybe the baby is simply cold and should be snuggling on mom’s chest.
Or maybe that baby has overwhelming infection, congenital heart disease, lung
disease, liver disease or is otherwise really sick. Kids with low blood
sugar and symptoms can have awful neurological problems. We need to investigate,
with urgency, the reason that the baby could not make a normal metabolic
blood sugar with no symptoms. Not an issue.
Breastmilk meets the nutritional requirements of healthy, term infants and those
same healthy term exclusively breastfed infants do not develop low
blood sugar because they are not eating. Healthy term infants do not need to
have their blood sugar screened.
blood sugar with symptoms: Big problem.
These children have some reason they can’t make up for low blood sugar with
other fuels. They may be, among other things, premature, small for
gestational age, an infant of a diabetic mother (especially if the diabetes was
poorly controlled), be sick, or be withdrawing from a substance mom was taking.
Those kids should be screened because then, the number means something.
American Academy of Pediatrics addressed this issue of newborn hypoglycemia in
with a clinical report which acknowledges many of the things that we don't
know about low blood sugar such as what glucose concentration in the newborn is
considered normal and how long the glucose needs to be low in order to cause
neurologic injury. In the clinical report, the authors created an
algorithm to help target at-risk children. The kids they recommend we screen are
only in three categories: small for gestational age babies; babies of diabetic
mothers (and controversially) large for gestational age infants; late preterm
babies, defined as those born at 34- 36 6/7 weeks. No other baby needs to
be screened. Here it is:
Jenny Thomas, MD, MPH, IBCLC, FAAP, FABM