Recognizing and Managing Gestational Diabetes

In order to differentiate between preexisting diabetes (Type 1 or Type 2) and gestational diabetes mellitus, it is recommended that women with risk factors for diabetes be tested at their first prenatal visit in their first trimester using standard diagnostic criteria. In comparison, gestational diabetes mellitus (GDM) is first diagnosed in the second or third trimester in women without a prior diagnosis of diabetes.

The prevalence of GDM varies depending on the screening and diagnostic approach used. Currently, there are two strategies identified in the American Diabetes Association's Standards of Medical Care in Diabetes - 2020 for diagnosis of GDM. They are known as the "one-step" and "two-step" approaches, and it is recommended that one of these tests be performed at 24 to 28 weeks of gestation in women without preexisting diabetes.

The "One-step" strategy (based on criteria from the International Association of the Diabetes and Pregnancy Study Groups (IADPSG)) involves a 75-gram oral glucose tolerance test (OGTT), which is performed with a plasma glucose measurement fasting and at one and two hours. The test is recommended to be performed in the morning after an overnight fast of at least eight hours.

The "Two-step" strategy (based on a National Institutes of Health (NIH) consensus panel) features a 50-gram glucose load (nonfasting) with plasma glucose measurements at 1 hour (Step 1); and if the plasma glucose test is ≥130 mg/dL, 135 mg/dL, or 140 mg/dL (7.2 mmol/L, 7.5 mmol/L, or 7.8 mmol/L, respectively), it is followed by the 100-gram OGTT (Step 2), which is performed when the patient is fasting.

Regardless of the criteria used to diagnose GDM, scientific evidence supports the effectiveness of Medical Nutrition Therapy (MNT) to improve maternal and neonatal outcomes. The Academy of Nutrition and Dietetics GDM Evidence-Based Nutrition Practice Guideline recommends that all women who are diagnosed with GDM be referred to a registered dietitian nutritionist (RDN) for individualized MNT.

Although no optimal frequency or duration of MNT encounters have been identified, "regular and frequent" sessions throughout the pregnancy are indicated for improved outcomes relating to glycemic control and appropriate weight gain, while meeting nutrient requirements.

The RDN plays an integral role on the interdisciplinary healthcare team by creating a personalized nutrition prescription which focuses on adequate calorie intake from a variety of healthy food choices to support pregnancy needs in women with GDM, and the GDM evidence-based nutrition practice guidelines provide MNT recommendations for its management.

References:

• Academy of Nutrition and Dietetics Nutrition Care Manual. Gestational Diabetes. Accessed October 28, 2020.
• American Diabetes Association. 2. Classification and diagnosis of diabetes. Diabetes Care. 2020; 43: S14–S31
• Duarte-Gardea MO, Gonzales-Pacheco DM, Reader DM, Thomas AM, Wang SR, Gregory RP, et al. Academy of Nutrition and Dietetics Gestational Diabetes Evidence-Based Nutrition Practice Guideline. J Acad Nutr Diet. 2018;118:1719–1742.
• Academy of Nutrition and Dietetics Evidence Analysis Library. 2016 Gestational Diabetes Mellitus (GDM) Guideline. Accessed 30 May 2019.