Laboratory diagnosis of overt type 2 diabetes in the first trimester of pregnancy

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The early detection and management of type 2 diabetes as well as gestational diabetes have the potential to greatly reduce the effects of the hyperglycemic environment on a growing fetus. Historically, diagnosis of gestational diabetes has included a glucose tolerance test (GTT) between 24 and 28 weeks of gestation. Type 2 diabetes is a similar, but different hyperglycemic state that a woman may experience as a pre‐existing state prior to becoming pregnant. Although both conditions are considered to be under the larger umbrella diagnosis of diabetes, their etiologies are quite different. If a woman is found to be hyperglycemic before pregnancy or early in the first trimester, she should receive the diagnosis of type 2 diabetes. If the hyperglycemic state is found in the second trimester, it confirms the diagnosis of gestational diabetes caused the physiologic changes of the pregnancy itself.
The recommended testing for diagnosis of overt type 2 diabetes in early pregnancy has recently become an issue of debate. Most clinics use a risk assessment to stratify pregnant women for overt diabetes testing in the first trimester. The first trimester testing does not detect gestational diabetes, but does detect pre‐existing or otherwise referred to as overt diabetes. The first trimester testing is performed in addition to the traditional gestational diabetes testing later on in the pregnancy. These two tests are performed to detect two different but similar conditions. The first of these conditions is the undiagnosed diabetic patient that has become pregnant, and the second diagnosis focuses on the pregnant patient who has developed a diabetic state as a result of the pregnancy. Although the human body reacts to both conditions in a similar way, they have two different etiologies each needing different treatment after the pregnancy has been completed and the baby delivered.
Currently the American College of Obstetricians and Gynecologists recommends a 1‐h glucose tolerance test (1GTT) in the first trimester for patients who are at risk for pre‐existing diabetes. Patients meeting specific risk factor criteria (see Table 1) are asked to undergo the 1GTT to detect overt diabetes in the first trimester (Coustan & Jovanovic, 2012). The test requires patients to drink a glucose load and wait in the clinic or laboratory for 1 h for a blood draw. According to the American Dietetic Association, the much more convenient hemoglobin A1C is an acceptable blood test to detect type 2 diabetes in the general population. Many experienced and respected clinicians are moving to the hemoglobin A1C with a value of equivalent or above 6.5% diagnostic for pre‐existing diabetes in the first trimester (Coustan, Nathan, & Barrs, 2016). Rationale includes the typically lower glucose threshold in early pregnancy, and the elevated value as highly sensitive for detecting abnormalities in glucose control within the last 3 months prior to the gestational onset. If the hemoglobin A1C is found to be at or above 6.5%, Coustan et al. (2016) recommend follow‐up screening with a more sensitive 2‐h GTT, which has also been recommended by the American Diabetes Association.
Clinicians and patients alike understand that the hemoglobin A1C is a quick and easy finger stick or one‐time blood draw that does not require that a patient drink a glucose load and requires only a few minutes of time. Results are also available to the provider and patient within a more rapid time frame for diagnosis and treatment decisions to occur.

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