For many moms-to-be with type 2 diabetes, failure to get a proper diagnosis on time results in unhealthy pregnancies and unhealthy babies.

The good news is that a study published by the American Diabetes Association (Diabetes Care, 2014) demonstrates that a simple blood test known as the hemoglobin A1c (sugar-bound hemoglobin, or HbA1c) can uncover hidden type 2 diabetes in expecting mothers. The study found that the A1c test can accurately detect undiagnosed type 2 diabetes in pregnant women.

“The problem is that we did not know reliable ways to screen for pre-existing diabetes early in pregnancy,” says  Florence Brown, M.D., Co-director of the Joslin-Beth Israel Deaconess Diabetes in Pregnancy Program

The hemoglobin A1c done early in pregnancy may be a convenient and effective way to identify women with pre-existing type 2 diabetes or who are at greater risk of worse pregnancy outcomes.

Florence Brown, MD
Director, Pregnancy Program

In this study, researchers examined the use of an A1c measurement done during the first trimester as a screening tool for pre-existing diabetes. The test was performed on more than 16,000 pregnant women and compared with the results of a 2-hour oral glucose tolerance test (OGTT), which is performed after an overnight fast, and is the gold standard diagnostic test for type 2 diabetes.

The A1c test measures the average blood sugar levels over a longer period of time, showing whether your blood sugar is staying under control for up to three months. Considered the standard diagnostic method, the American Diabetes Association uses the A1c target of 6.5 percent for diagnosing type 2 diabetes in those who are not pregnant. An A1c between 5.7 and 6.4 is considered pre-diabetic.

The study found that the hemoglobin A1c test was able to identify all the women with pre-existing type 2 diabetes when an A1c cutoff point of 5.9 percent was used, says Dr. Brown. “In addition, even if women did not have a preexisting diabetes, the A1c cutoff point of 5.9 was able identify a population of women at greater risk for adverse pregnancy outcomes, including some women with gestational diabetes.”

This is an important finding because 5.9 percent is considerably lower than the value of 6.5 percent currently used to diagnose patients with type 2 diabetes who are not pregnant, she adds. The 6.5 percent threshold would have missed almost half of these women and is therefore too high for screening purposes, the study authors conclude.

Mothers who have pre-existing diabetes, either type 2 or type 1, during pregnancy face an increased risk of complications. This study also found that an early pregnancy A1c of 5.9 percent to 6.4 percent was associated with a greater risk of worse pregnancy outcomes, including birth defects, preeclampsia and perinatal death.

Properly diagnosing expecting mothers early on will allow doctors to recommend changes to help women keep their blood sugar at safe levels. Adopting lifestyle changes – such as healthy eating and exercise – is good for both moms-to-be and their babies.

Who Should Get Tested

Given that the prevalence of type 2 diabetes is increasing, the A1c test done as early as possible could identify women at high risk and improve pregnancy outcomes. “This study supports the use of an A1c test in the first trimester and ideally with the first prenatal visit as one possible screen for pregnant women,” says Dr. Brown.

In addition, all pregnant women should undergo screening for gestational diabetes routinely at 24 to 28 weeks, says Dr. Brown. “A one step 75 gram 2-hour oral glucose tolerance test, endorsed by the American Diabetes Association and the Endocrine Society, is one method. Alternatively, a two-step method using a 50 gram glucose challenge test followed by a 3-hour 100 gram oral glucose tolerance test is endorsed by the American College of Obstetrics and Gynecology.”

If you have diabetes and are pregnant, or are thinking about becoming pregnant, visit the Joslin's Pregnancy clinic for more information or to make an appointment.