Blood test promising for detecting gestational diabetes

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A simple blood test given as early as 10 weeks into pregnancy may help identify women at risk for gestational diabetes, thus allowing for lifestyle changes before the disorder develops.

Researchers for the blood test study in Scientific Reports assessed whether the HbA1c test (also called the A1C test), which is commonly used to diagnose type 2 diabetes, could identify signs of gestational diabetes in the first trimester of pregnancy. 

The test roughly calculates the average blood glucose levels over the previous 2 to 3 months, based on the amount of glucose that has accumulated on the surface of red blood cells. 

“We wanted to identify women at high risk for gestational diabetes early in pregnancy so that it leaves more time to intervene to prevent the condition,” said senior author Cuilin Zhang MD, PhD, a senior investigator in the Epidemiology Branch of the Division of Intramural Population Health Research at the National Institutes of Health’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) in Bethesda, Maryland.

The few studies to date that have examined whether the HbA1c test can help flag the risk for gestational diabetes have been limited to women already at high risk for the condition. The test is also not currently recommended to diagnose gestational diabetes at any stage in pregnancy.

The researchers of the current study analyzed records from the NICHD Fetal Growth Study, which was a large observational trial that recruited more than 2,000 low-risk pregnant women from 12 U.S. clinical sites between 2009 and 2013. 

HbA1c test results from 107 women who later developed gestational diabetes were compared to the test results from 214 women who did not develop the disorder. Most of the women had the test performed at four intervals during their pregnancy: early (weeks 8-13), middle (weeks 16-22 and weeks 24-29) and late (weeks 34-37).

“Women who went on to develop gestational diabetes had higher HbA1c levels with an average of 5.3% in the first trimester, compared to those without gestational diabetes whose average HbA1c level was 5.1%,” Dr. Zhang told Contemporary OB/GYN. “Moreover, first trimester HbA1c significantly improved the prediction of gestational diabetes over conventional risk factors.”

Further, each 0.1% increase in HbA1c above 5.1% in early pregnancy was associated with a 22% higher risk for gestational diabetes; however, in middle pregnancy, HbA1c levels declined in both groups, only to increase again in the last third of pregnancy.

“This latter rise is consistent with the decrease in sensitivity to insulin that often occurs during the third trimester,” Dr. Zhang said.

Dr. Zhang said the results were mostly expected. “Data from our previous work showed that prepregnancy and early pregnancy time windows are relevant to gestational diabetes risk,” she said. “HbA1c levels usually reflect glucose control status over the past 2 to 3 months. For the current study, the first trimester sample was collected at between 8 and 13 weeks, when HbA1c levels reflected glucose control status before pregnancy or during the first week of pregnancy.”

Dr. Zhang said study results suggest that the HbA1C test could potentially help identify women at higher risk for gestational diabetes early in pregnancy, for which lifestyle changes like exercise and a healthy diet might be effective in reducing that risk.

“If our findings are confirmed by future studies, clinicians may consider testing women for HbA1c in early pregnancy,” Dr. Zhang said.