From the Guidelines
Diabetes screening in pregnancy should typically occur between 24-28 weeks of gestation using a glucose challenge test (GCT) or oral glucose tolerance test (OGTT) 1. For women with risk factors such as obesity, family history of diabetes, previous gestational diabetes, or certain ethnic backgrounds, screening may be done earlier, often at the first prenatal visit. The standard screening involves drinking a glucose solution (usually 50g) and measuring blood glucose levels one hour later. If results are elevated (typically above 140 mg/dL), a follow-up 3-hour OGTT with 100g glucose is performed for diagnosis. For high-risk women, hemoglobin A1C or fasting glucose may be checked at the first prenatal visit. Early detection and management of gestational diabetes is crucial as it can lead to complications like macrosomia (large baby), birth injuries, neonatal hypoglycemia, and increased risk of cesarean delivery. Regular monitoring throughout pregnancy helps ensure appropriate treatment through diet, exercise, and sometimes insulin or oral medications to maintain normal blood glucose levels.
Some key points to consider:
- The USPSTF concludes with moderate certainty that there is a moderate net benefit to screening for gestational diabetes after 24 weeks of gestation to reduce maternal and fetal complications 1.
- The evidence on screening for gestational diabetes before 24 weeks of gestation is insufficient, and the balance of benefits and harms of screening cannot be determined 1.
- Initial treatment includes moderate physical activity, dietary changes, support from diabetes educators and nutritionists, and glucose monitoring 1.
- If the patient's glucose is not controlled after these initial interventions, she may be prescribed medication (either insulin or oral hypoglycemic agents) or have increased surveillance in prenatal care or changes in delivery management 1.
From the Research
Screening for Gestational Diabetes
- Screening for gestational diabetes is typically performed between 24 and 28 weeks of pregnancy 2, 3
- The American College of Obstetricians and Gynecologists recommends screening for gestational diabetes at 24-28 weeks of gestation, but earlier screening may be necessary for high-risk women 3
- A 75g oral glucose tolerance test (OGTT) is commonly used for screening and diagnosis of gestational diabetes 2, 4
Diagnosis of Gestational Diabetes
- The 75g OGTT is a one-step approach that provides a faster diagnosis time, better tolerance, and is easier to remember than the two-step approach 2
- The diagnostic threshold for gestational diabetes is a plasma glucose level exceeding 5.1 mmol/L at 0h, 10.0 mmol/L at 1h, and 8.5 mmol/L at 2h 5
- Abnormal plasma glucose levels at different time points in the OGTT are associated with an increased risk of adverse pregnancy outcomes 5
Risk Factors for Gestational Diabetes
- Maternal overweight and obesity, later age at childbearing, previous history of gestational diabetes, family history of type 2 diabetes, and ethnicity are major risk factors for gestational diabetes 4
- Older and obese women are at higher risk of gestational diabetes and may require earlier screening and intervention 6
- Maternal age and HbA1c levels are significantly associated with fetal abdominal overgrowth in women with gestational diabetes 6
Timing of Screening
- Screening for gestational diabetes at 24-28 weeks of gestation may be too late for older and obese women, who may require earlier screening and intervention 6
- Earlier screening may be necessary for high-risk women, but the benefit of screening for gestational diabetes during early pregnancy has not been supported by prospective studies 3