Diagnosing Gestational Diabetes

Timing of Screening

The American College of Obstetricians and Gynecologists recommends that all pregnant women not previously known to have diabetes should be screened for gestational diabetes mellitus (GDM) at 24-28 weeks of gestation 1, 2
Women with risk factors, such as a body mass index (BMI) of 30 kg/m² or higher, history of previous GDM, family history of diabetes, or high-risk ethnicity, should be tested for undiagnosed type 2 diabetes at the first prenatal visit 3, 1
Risk factors warranting early screening include a history of delivering a macrosomic baby, history of polycystic ovary syndrome, and high-risk ethnicity 4

The one-step strategy involves performing a 75g oral glucose tolerance test (OGTT) with plasma glucose measurements when the patient is fasting and at 1 and 2 hours, and diagnosis of GDM is made when any of the following plasma glucose values are met or exceeded: fasting 92 mg/dL, 1 hour 180 mg/dL, or 2 hour 153 mg/dL 1, 2
The two-step strategy involves an initial 50g glucose load test, followed by a 100g OGTT if the plasma glucose level is 130-140 mg/dL or higher, and diagnosis of GDM is made if at least two of the following four plasma glucose levels are met or exceeded: fasting 95 mg/dL, 1 hour 180 mg/dL, 2 hour 155 mg/dL, or 3 hour 140 mg/dL 1, 2
The American College of Obstetricians and Gynecologists currently supports the two-step approach 2

Women with GDM should be screened for persistent diabetes at 4-12 weeks postpartum using a 75g OGTT 1, 4
Women with a history of GDM should have lifelong screening for diabetes or prediabetes at least every 3 years 1, 4
Women found to have prediabetes should receive intensive lifestyle interventions or metformin to prevent diabetes 1, 4