Children who experience a brief drop in blood sugar right after birth may have a harder time with reading and math when they go to school, a new study suggests.
The study, of nearly 1,400 fourth-graders, found that kids who had so-called “transient hypoglycemia” as newborns typically had poorer reading and math skills than their peers.
Experts stressed that the findings show only a correlation, and do not prove cause and effect.
But the study, published online Aug. 24 in the journal JAMA Pediatrics, could add to a long-standing controversy over transient hypoglycemia.
The term refers to cases where an infant’s blood sugar drops to an abnormally low level within three hours after birth, but quickly recovers. Experts have long been divided over its significance in otherwise healthy, full-term infants.
The newborn brain needs glucose (sugar) for energy, and it’s known that prolonged hypoglycemia can cause irreversible brain damage in infants. Because of that, newborns at high risk of severe hypoglycemia have their blood sugar screened soon after birth.
That includes babies who are preterm, abnormally small or large, or born to moms with diabetes, said Dr. Jane Harding, a professor of neonatology at the University of Auckland in New Zealand.
“We’ve found that about half of babies at [high] risk do, in fact, become hypoglycemic,” said Harding, co-author of an editorial published with the study.
But when it comes to other newborns, guidelines from the American Academy of Pediatrics advise against routine blood sugar screening.
The new findings are not enough to change those guidelines, said lead researcher Dr. Jeffrey Kaiser, of Baylor College of Medicine in Houston.
“We have to be very careful about interpreting this, because it’s retrospective data from a single medical center,” he said. “This is just one piece of the puzzle.”
But given the possibility this study raises — that even transient hypoglycemia could harm infants’ brains — more research is needed, Kaiser said.
“I hope other researchers will look into this and see if they replicate our findings,” he said.
The results are based on records from 1,395 children born in 1998 at the University of Arkansas, which had a policy of screening all newborns for hypoglycemia. Kaiser’s team matched the children’s medical records with their school records to see whether short-lived hypoglycemia showed any correlation with standardized test scores in fourth grade.
They found that from 6 percent to 19 percent of the children had suffered transient hypoglycemia as newborns, depending on the definition of “low” blood sugar. And those kids were roughly half as likely to perform at grade level on tests of math and literacy.
For example, 6 percent of children had had a single blood sugar measurement drop below 35 mg/dL soon after birth. Of those children, 32 percent performed at grade level on literacy tests, compared with 57 percent of other children.
The problem, though, is that many things happen in a child’s life between birth and fourth grade. Kaiser said his team did account for factors like children’s birth weight and mothers’ education levels.
“But we couldn’t control for what happened to those children over the next 10 years,” he said. “We don’t know if their parents read to them. We don’t know what their nutrition was like.”
Plus, Kaiser said, transient hypoglycemia might simply be a “marker” of some other problem that occurred during fetal brain development. If that’s the case, it’s not clear that detecting and treating low blood sugar would be helpful.
The academy guidelines suggest treating transient hypoglycemia with earlier bottle- or breast-feeding, or IV glucose. But Kaiser said there is little evidence that this prevents any ill effects on the brain.
Harding agreed that it’s too soon for routine, universal screening of newborns. One reason is, there are potential harms.
“Pain-induced stress,” from needle sticks, may affect newborn brain development, Harding said. And if treatment causes blood sugar to spike, that itself could worsen any brain damage.
For now, Harding said, the “safest approach” is to screen high-risk newborns only.
As for prevention, Kaiser said that when mothers have diabetes, good blood sugar control can reduce the risk of newborn hypoglycemia. Other than that, he said, there are no established ways to prevent the problem.
The American Academy of Pediatrics has more on supporting children’s early brain development.