Elevated blood sugar levels during pregnancy may result in poorer birth outcomes

UNIVERSITY PARK, Pa. — Pregnant women in the United States are routinely tested for gestational diabetes, a condition where the body has high blood sugar during pregnancy that can lead to health problems for both mothers and babies. But even when the mother has not reached the threshold for gestational diabetes, higher levels of blood sugar during pregnancy may result in poorer birth outcomes, according to a new study led by Penn State researchers.

Pregnant women in the U.S. are typically screened for gestational diabetes with a glucose challenge test, where they consume a very sugary drink and have their blood sugar levels monitored after one hour. If their levels spike beyond acceptable values, they fail and take a longer glucose test after fasting. Failing this second test results in a diagnosis of gestational diabetes, but those who fail the first test and pass the second are usually treated as though there is no risk.

In a recent study published in The American Journal of Clinical Nutrition, the researchers examined records from thousands of births and found that failing the glucose challenge test was associated with babies with higher birth weights — a risk factor for future obesity and diabetes — even when women passed their second glucose test.

“There appears to be risk associated with higher blood glucose levels even without a diagnosis of gestational diabetes, at least for some pregnancies,” said Alison Gernand, associate professor of nutritional sciences at Penn State and corresponding author of this study. “We want obstetricians and other medical professionals to be aware that mothers’ elevated blood glucose levels may have the implications for the health of babies.”

The researchers analyzed information from 10,899 births where the placenta was sent for pathological examination between 2011 and 2022 at Northwestern Memorial Hospital in Chicago. The dataset represents 20% of all births at the hospital during these years, which is close to the national average of births where the placenta is sent for further evaluation.

The researchers limited their analyses to births where the placenta was sent to pathology and the mother failed the glucose challenge test because they were also interested in the way that blood sugar might affect the placenta. Typically, placentas are evaluated when physicians are concerned that there may be complications for the mother or baby, but they are not sent to pathology specifically for gestational diabetes.

These data were available thanks to the efforts of co-author Jeffery Goldstein, director of perinatal pathology at Northwestern University’s Feinberg School of Medicine. He collected the data as co-principal investigator of the PlacentaVision study, a large National Institutes of Health-funded project to develop an assessment tool for the placenta.

Births where more than one child was delivered were excluded from the study.

Mothers in the study were divided into three groups. Those who passed their glucose challenge test and were not diagnosed with gestational diabetes comprised 78% of the participants. Those who failed their glucose challenge test and were not diagnosed with gestational diabetes comprised 17% of the participants. Those who failed their glucose challenge test and were diagnosed with gestational diabetes comprised 5% of the participants.

For each birth, the researchers examined gestational age — how long the pregnancy lasted before the baby was born — the birth weight relative to the length of the pregnancy, the ratio between the weight of the baby and the weight of the placenta and whether the baby was born preterm.

Compared to women who passed their glucose challenge test, those who failed but were not diagnosed with gestational diabetes were 41% more likely to give birth to babies who were large for their gestational ages and were slightly more likely to give birth before their babies reached full term.

Women who were diagnosed with gestational diabetes, meanwhile, were 71% more likely to give birth to babies who were large for their gestational ages compared to women who passed their glucose challenge test.

Babies who are large for their gestational age are at higher risk for diabetes and obesity later in life, so these differences represent a meaningful risk, the researchers said.

“The current cutoffs for glucose values are helpful to make a diagnosis of gestational diabetes, but glucose values are on a continuum, and — based on these results — clinical outcomes might also be on a continuum,” said Kelly Gallagher, assistant research professor of nursing at Penn State and co-author of the study.

The researchers said they have no reason to suspect outcomes would be different for births when placentas weren’t sent to pathology. To more fully understand the blood sugar impacts in all pregnancies, however, they said the study would need to be replicated with all births, not just births where the placenta was sent to pathology.

“In medicine, we often look at clinical thresholds as black and white; you either have gestational diabetes or you don’t,” said Amrita Arcot, first author of the study who completed the research as doctoral candidate in nutritional sciences at Penn State and is now a postdoctoral fellow at Tulane University. “Seventeen percent of the women in this study, however, live in a grey area where there is no diagnosis, but risk still exists. This risk can impact mothers and babies immediately and for years. Mothers need to be aware that elevated blood sugar levels may affect their baby, even without a diagnosis.”

These results provide more evidence that pregnant women should have access to nutritional guidance early in pregnancy when there is time to improve outcomes, the researchers said.

“Pregnancy is a critical time for nutritional health, but women are only connected with dietitians after they are diagnosed with gestational diabetes,” Gernand said. “If everyone who was pregnant saw a dietitian as part of their clinical care, we could help people support their health — and their baby’s health — in many ways, including maintaining healthy blood sugar.”

This research was funded by the National Institutes of Health National Institute of Biomedical Imaging and Bioengineering.

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