Diagnóstico de Diabetes Gestacional

Enfoque de Un Paso

• El enfoque de un paso para el diagnóstico de diabetes gestacional, recomendado por la Asociación Internacional de Grupos de Estudio de Diabetes y Embarazo (IADPSG), utiliza una prueba de tolerancia oral a la glucosa (PTOG) de 75 g, con mediciones de glucosa en ayunas, a la hora y a las 2 horas, entre las semanas 24-28 de gestación, y diagnostica la diabetes gestacional cuando se cumple o excede cualquiera de los siguientes valores de glucosa plasmática: ayunas 92 mg/dL, 1 hora 180 mg/dL, o 2 horas 153 mg/dL 1, 2
• Este enfoque identifica aproximadamente 2-3 veces más casos de diabetes gestacional que el enfoque de dos pasos, con una prevalencia de 15-20% versus 5-6% 3

Enfoque de Dos Pasos

• El enfoque de dos pasos para el diagnóstico de diabetes gestacional comienza con una prueba de desafío de glucosa de 50 g, seguida de una PTOG de 100 g en casos positivos, y diagnostica la diabetes gestacional cuando se cumplen o exceden al menos dos de los siguientes valores de glucosa plasmática: ayunas 95 mg/dL, 1 hora 180 mg/dL, 2 horas 155 mg/dL, o 3 horas 140 mg/dL 4, 1, 5
• La prueba de desafío de glucosa de 50 g no requiere ayuno y es más fácil de implementar, mientras que el enfoque de un paso requiere que todas las mujeres estén en ayunas 2

Consideraciones Clínicas

• El Colegio Americano de Obstetras y Ginecólogos (ACOG) actualmente apoya el enfoque de dos pasos, pero señala que un solo valor elevado puede utilizarse para el diagnóstico de diabetes gestacional 1, 5
• Las mujeres con diabetes gestacional deben ser evaluadas para detectar diabetes persistente entre 4-12 semanas posparto mediante una PTOG de 75 g 3
• La elección entre los dos enfoques sigue siendo controvertida y puede depender de factores como la prevalencia de diabetes gestacional en la población, los recursos disponibles y las consideraciones de costo-efectividad 5

Glucose Tolerance Test Measurement Intervals

Diagnostic Criteria and Testing Protocols

• The standard interval for a Glucose Tolerance Test (GTT) is fasting, 1 hour, 2 hours, and 3 hours (for the 100g test), with measurements taken at these specific time points after glucose load administration, as recommended by the American Academy of Family Physicians and the American Diabetes Association 6, 7, 8
• Measurements are taken at three time points: fasting, 1 hour, and 2 hours after a 75g glucose load, according to the American Diabetes Association 7, 8, 9
• The test should be performed in the morning after an overnight fast of at least 8 hours, as suggested by the American Diabetes Association 8, 10
• Diagnosis of gestational diabetes mellitus (GDM) is made when any of the following values are met or exceeded: Fasting: 92 mg/dL, 1 hour: 180 mg/dL, 2 hours: 153 mg/dL, based on guidelines from the American Diabetes Association 8, 10
• The American Diabetes Association recommends a two-step strategy for GDM screening, starting with a 50g glucose load test (GLT) with measurement at 1 hour only (nonfasting), followed by a 100g OGTT if the 1-hour value is elevated 7, 11
• The American Diabetes Association suggests the following diagnostic criteria for 100g OGTT (Carpenter-Coustan): Fasting: 95 mg/dL, 1 hour: 180 mg/dL, 2 hour: 155 mg/dL, 3 hour: 140 mg/dL 12, 11
• Current guidelines from the American Diabetes Association still recommend the complete protocol with all time points for diagnosing GDM 7, 8
• The American Academy of Family Physicians considers the 75g OGTT as the reference standard for diabetes diagnosis 6
• The American Diabetes Association recommends the full protocol (either one-step or two-step) for gestational diabetes screening at 24-28 weeks gestation 7, 12

Diagnostic Criteria for Diabetes Using the 75g Oral Glucose Tolerance Test (OGTT)

Primary Indication: Gestational Diabetes Screening

• The International Association of Diabetes and Pregnancy Study Groups (IADPSG) and the American Diabetes Association recommend performing the 75g OGTT at 24-28 weeks of gestation in pregnant women not previously diagnosed with diabetes, using the one-step diagnostic approach 13
• The test should be performed in the morning after an overnight fast of at least 8 hours, with plasma glucose measured at three time points: fasting, 1 hour, and 2 hours after the 75g glucose load 13, 14, 15
• The diagnosis of gestational diabetes is made when any single value meets or exceeds the following thresholds: fasting ≥92 mg/dL, with the American College of Obstetricians and Gynecologists supporting a single elevated value for diagnosis 13, 14

Secondary Indication: Diagnosing Diabetes Outside Pregnancy

• The 75g OGTT can be used to diagnose diabetes in non-pregnant adults when fasting plasma glucose is <126 mg/dL but clinical suspicion for diabetes remains high, with the European Heart Journal recommending diagnostic criteria 15
• Fasting plasma glucose ≥126 mg/dL or 2-hour post-load glucose ≥200 mg/dL indicates diabetes, according to the European Heart Journal 15
• Impaired glucose tolerance is diagnosed when 2-hour glucose is ≥140 mg/dL but <200 mg/dL, as recommended by the European Heart Journal 15

Important Clinical Considerations

• The American Diabetes Association recommends that women diagnosed with gestational diabetes undergo a 75g OGTT at 4-12 weeks postpartum to screen for persistent diabetes or prediabetes, with a 3.4-fold increased risk of developing type 2 diabetes 13
• The European Heart Journal recommends avoiding the 75g OGTT in patients who cannot tolerate oral glucose loads 15
• The American College of Cardiology is not mentioned in this context, however the American Diabetes Association and the International Association of Diabetes and Pregnancy Study Groups provide guidelines for the 75g OGTT 13

Guidelines for the 3-Hour Glucose Tolerance Test in Pregnancy

Diagnostic Criteria and Test Administration

• The American College of Obstetricians and Gynecologists (ACOG) recommends a 3-hour, 100-gram oral glucose tolerance test (OGTT) as the second step in the two-step approach to diagnose gestational diabetes mellitus (GDM), requiring at least two of four elevated values to confirm the diagnosis 16, 17, 18
• The 3-hour OGTT is indicated for pregnant women with a positive 50-gram, 1-hour glucose loading test (GLT) screening result at 24-28 weeks gestation, with a screening threshold of ≥140 mg/dL (7.8 mmol/L), though ACOG recommends ≥135 mg/dL (7.5 mmol/L) in high-risk ethnic populations 16, 17, 18
• The test must be performed after an overnight fast of at least 8 hours 16, 17, 18

Diagnostic Thresholds

• GDM is diagnosed when at least two of the four values meet or exceed the following thresholds: fasting ≥95 mg/dL (5.3 mmol/L), 1-hour ≥180 mg/dL (10.0 mmol/L), 2-hour ≥155 mg/dL (8.6 mmol/L), and 3-hour ≥140 mg/dL (7.8 mmol/L) 16, 17, 18, 19
• Alternative NDDG criteria: fasting ≥105 mg/dL (5.8 mmol/L), 1-hour ≥190 mg/dL (10.6 mmol/L), 2-hour ≥165 mg/dL (9.2 mmol/L), and 3-hour ≥145 mg/dL (8.0 mmol/L) 16, 17, 18

Treatment and Management

• Treatment of GDM diagnosed by the two-step approach reduces neonatal macrosomia, large-for-gestational-age births, and shoulder dystocia without increasing small-for-gestational-age births 19
• All women diagnosed with GDM must undergo a 75-gram OGTT at 4-12 weeks postpartum to assess for persistent diabetes 16

Diagnosis and Management of Gestational Diabetes Using the 3‑Hour 100‑g OGTT

Diagnostic Criteria

• The Carpenter‑Coustan criteria define an abnormal 3‑hour 100‑g OGTT when at least two of the four plasma glucose measurements meet or exceed the following thresholds: fasting ≥ 95 mg/dL (5.3 mmol/L), 1‑hour ≥ 180 mg/dL (10.0 mmol/L), 2‑hour ≥ 155 mg/dL (8.6 mmol/L), and 3‑hour ≥ 140 mg/dL (7.8 mmol/L)【20】【21】【22】【23】.

• Initial screening for gestational diabetes mellitus (GDM) is performed with a 50‑g glucose loading test between 24–28 weeks of gestation (non‑fasting)【20】【22】.

• If the 1‑hour plasma glucose from the screening test is ≥ 130 mg/dL, ≥ 135 mg/dL, or ≥ 140 mg/dL, a diagnostic 3‑hour OGTT is indicated【20】【22】.

• The diagnostic 100‑g OGTT must be conducted after an overnight fast of at least 8 hours【20】【22】【23】.

• Blood samples for the OGTT are drawn at four time points: fasting, 1 hour, 2 hours, and 3 hours after glucose ingestion【20】【21】.

• The American College of Obstetricians and Gynecologists (ACOG) acknowledges that a single elevated value can be used for diagnosis, although the traditional Carpenter‑Coustan rule requires two abnormal values【20】【22】【23】.

• The older National Diabetes Data Group (NDDG) criteria use higher glucose thresholds (fasting ≥ 105 mg/dL, 1‑hour ≥ 190 mg/dL, 2‑hour ≥ 165 mg/dL, 3‑hour ≥ 145 mg/dL); however, the Carpenter‑Coustan criteria are more widely adopted and identify a greater number of at‑risk women【22】【20】.

Clinical Considerations

• Women who meet only one abnormal value on the 3‑hour OGTT have substantially increased risks for adverse pregnancy outcomes (e.g., macrosomia, large‑for‑gestational‑age infants, neonatal hypoglycemia, cesarean delivery, and pregnancy‑induced hypertension) that are comparable to those diagnosed with full‑criteria GDM【20】【22】【23】.

Test Preparation

• Proper preparation requires the patient to fast for at least 8 hours before the OGTT【20】【22】【23】.

• The test should be scheduled in the morning to minimize variability【20】.

• Failure to adhere to fasting and timing protocols can result in inaccurate glucose measurements【20】.

Postpartum Follow‑Up

• All women diagnosed with GDM should undergo a 75‑g OGTT between 4 and 12 weeks postpartum to evaluate for persistent diabetes【20】【23】.

• Women with a history of GDM have an approximately 3.4‑fold increased risk of developing type 2 diabetes later in life【20】.

Prevalence and Impact

• The two‑step screening approach (50‑g GLT followed by 100‑g OGTT) identifies about 5–6 % of pregnant women with GDM, whereas the one‑step 75‑g OGTT approach identifies approximately 15–20 %【20】.

• The two‑step method is currently endorsed by ACOG as the preferred screening strategy for GDM【20】.