Manual of Clinical Nutrition Management C- 15 Copyright © 20 13 Compass Group, Inc.
MEDICAL NUTRITION THERAPY FOR GESTATIONAL DIABETES
MELLITUS AND PREGNANCY WITH PREEXISTING DIABETES MELLITUS
Overview
Previously, gestational diabetes mellitus (GDM) was defined as any degree of glucose intolerance with onset
or first recognition during pregnancy (1). In 2011, The American Diabetes Association revised the definition
along with new diagnostic criteria as a result of an increase in the incidence of pregnant women being
identified to have undiagnosed overt diabetes and studies demonstrating adverse maternal, fetal and
neonatal outcomes using previously established standards considered to be normal for pregnancy (1). It is
now recommended that women found to have diabetes at their first prenatal visit receive a diagnosis of overt,
not gestational diabetes (1,2). An increase in insulin-antagonist hormone levels and resulting insulin
resistance occurs in the second and third trimester of pregnancy. Women who are unable to produce
adequate insulin to maintain normal glucose concentrations during the second and third trimester are then
diagnosed with gestational diabetes mellitus (1,2). After delivery, in a majority of women with GDM blood
glucose will return to normal but these women are at increased risk of developing type 2 diabetes (1,2).
Nutrition Assessment and Diagnosis
The results of the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study, a large-scale,
multinational, epidemiologic study demonstrated that the risk of adverse maternal, fetal, and neonatal
outcomes continuously increased as a function of maternal glycemia at 24 to 28 weeks of gestation, even
within ranges previously considered to be normal for pregnancy (1). These results led to reconsideration of
the diagnostic criteria for GDM by an international consensus of multiple obstetrical and diabetes
organizations (1,2). The new criteria established in 2011 will significantly increase the prevalence of GDM,
primarily because only one abnormal value, not two is sufficient to make the diagnosis (1,2). With increasing
identification will come a greater demand for management and treatment of GDM. However, it is important
to note that 80 to 90% of newly diagnosed cases evaluated in these studies had mild GDM (whose glucose
values overlapped with the new thresholds), and likely can be managed with lifestyle therapy alone (1,2).
Women with risk factors for diabetes should be screened for undiagnosed type 2 diabetes at the first
prenatal visit using standard diagnostic criteria established by the American Diabetes Association (1,2). Risk
factors for screening include (1):
overweight (BMI > 25 kg/m^2 )
first-degree relative with diabetes
high-risk race/ethnic group for prevalence of diabetes
delivered a baby weight > 9 lbs or previous diagnosis of GDM
polycystic ovarian syndrome (PCOS)
A1C > 5.7%, impaired glucose tolerance (IGT), or impaired fasting glucose (IFG)on previous testing
All pregnant women not known to have diabetes, should be tested for GDM at 24 to 28 weeks of gestation
(1,2). The diagnosis of GDM is based on the results of the 75-g 2-hour oral glucose tolerance test (OGTT) with
plasma glucose measurement fasting and at 1 and 2 hours (2). The OGTT should be performed in the morning
over an overnight fast of at least 8 hours (2). Diagnosis of GDM is made when any of the following plasma
glucose values are exceeded (1,2):
Fasting: > 92 mg/dL (5.1 mmol/L)
1 hour: > 180 mg/dL (10.0 mmol/L)
2 hour: >153 mg/dL (8.5 mmol/L)
Because the A1C test reflects the glycemic profile in the last 10 weeks, it is not used to determine need for
additional therapy in GDM. It can however, be used in the first trimester to diagnose type 2 diabetes (A1C >
6.5%) (1,2). See Section II: Diagnostic Criteria for Diabetes Mellitus.
The American College of Obstetricians (ACOG) continues to recommend a 2-step approach to screening and
diagnosis. ACOG recommends all pregnant women be screened for GDM, whether patient history, clinical risk
factors, or a 50-g, 1-hour glucose challenge test at 24 to 28 weeks (3). The diagnosis of GDM is made based on
the result of the 100-g, 3-hour OGTT that requires two or more thresholds be met or exceed to make the