By Diagnostics World Staff
August 16, 2018 | A blood tests commonly used to diagnose Type 2 diabetes could identify women at risk for gestational diabetes as early as the 10th week of pregnancy according to researchers from the National Institute of Child Health and Human Development (NICHD). The results were published today in Scientific Reports (DOI: 10.1038/s41598-018-30833-8)
Gestational diabetes occurs only in pregnancy and results when the level of blood glucose rises too high. Gestational diabetes increases the mother’s chances for high blood pressure disorders of pregnancy and the need for cesarean delivery, and the risk for cardiovascular disease and type 2 diabetes later in life. For infants, gestational diabetes increases the risk for large birth size. Unless they have a known risk factor, such as obesity, women typically are screened for gestational diabetes between 24 and 28 weeks of pregnancy.
Researchers from NICHD evaluated previously-gathered data from the Fetal Growth Studies-Singleton Cohort, a large observational study of more than 2,000 low risk pregnant women from 12 U.S. clinical sites between 2009 and 2013. The researchers compared HbA1c test results from 107 women who later developed gestational diabetes to test results from 214 women who did not develop the condition. Most of the women had tests at four intervals during pregnancy: early (weeks 8-13), middle (weeks 16-22 and 24-29) and late (weeks 34-37).
The HbA1c test (also called the A1C test) approximates the average blood glucose levels over the previous 2 or 3 months, based on the amount of glucose that has accumulated on the surface of red blood cells.
Women who went on to develop gestational diabetes had higher HbA1c levels in the first trimester (an average of 5.3%), than those without gestational diabetes (an average HbA1c level of 5.1%). Each .1 percent increase in HbA1c above 5.1 in early pregnancy was associated with a 22% higher risk for gestational diabetes.
In the second trimester, HbA1c levels declined for both groups, and increased again in the third trimester, which is consistent with the decrease in sensitivity to insulin that often occurs during this time period.
“We observed a significant improvement in GDM prediction with the inclusion of first trimester HbA1c over conventional risk factors alone,” the authors write in the paper. “Thus, even in this cohort of low-risk women without pre-existing medical conditions, HbA1c measured in the first trimester improved GDM prediction.”
The authors note that the HbA1c test at the cutoff point they suggest—5.1%--has relatively low sensitivity but moderately high specificity. At the current cutoff point for diagnosing prediabetes outside of pregnancy, the specificity is very high (95%). HbA1c, then, would not be an appropriate replacement for the current second trimester glucose challenge test, but would also return few false positives in the first trimester for low-risk women.
“Future studies evaluating early intervention based on elevated first trimester HbA1c are essential to determine its utility,” the authors conclude, and additional research will help determine whether lowering HbA1c with lifestyle changes, either in early pregnancy or before pregnancy, could reduce the risk for the condition.