From the Guidelines
Screening for gestational diabetes mellitus (GDM) in a 24-year-old primigravida woman with no significant medical history should be performed between 24-28 weeks of gestation. This recommendation is based on the most recent and highest quality study, which suggests that screening at this time can help reduce maternal and fetal complications associated with GDM 1. The American Diabetes Association and the U.S. Preventive Services Task Force recommend screening for GDM at 24-28 weeks of gestation in pregnant women who have not been previously diagnosed with type 1 or 2 diabetes mellitus 1.
Key Considerations
- The patient's age and lack of risk factors do not necessitate early screening 1.
- The standard screening approach involves a 50-gram glucose challenge test, followed by a 3-hour 100-gram oral glucose tolerance test if the initial screen is abnormal 1.
- Screening before 24 weeks of gestation is not recommended unless the patient has high-risk factors, such as a history of GDM, family history of diabetes, or obesity 1.
- Education about healthy diet and exercise during pregnancy should be provided to all patients, regardless of their risk factors 1.
Screening Approach
- The 2-step approach involves a 50-g glucose challenge test, followed by a 100-g oral glucose tolerance test if the initial screen is abnormal 1.
- The 1-step approach involves a 75-g glucose load, with plasma glucose levels evaluated after 1 and 2 hours 1.
- The diagnosis of GDM is made when 2 or more glucose values fall at or above the specified glucose thresholds 1.
Benefits and Harms
- Screening for GDM has been shown to reduce maternal and fetal complications, including preeclampsia, macrosomia, and shoulder dystocia 1.
- The harms of screening and treatment are small to none, with no significant differences in cesarean delivery or neonatal intensive care unit admissions between women who were treated and women who were not treated for GDM 1.
From the Research
Screening for Gestational Diabetes Mellitus (GDM)
- The American College of Obstetricians and Gynecologists and other organizations recommend screening for GDM between 24 and 28 weeks of pregnancy 2, 3, 4, 5.
- A 24-year-old primigravida woman with no significant medical history should be screened for GDM at 24 weeks of gestation or after, as recommended by the US Preventive Services Task Force (USPSTF) 5.
- The USPSTF concludes that there is a moderate net benefit to screening for GDM at 24 weeks of gestation or after to improve maternal and fetal outcomes 5.
- However, the evidence on screening for GDM before 24 weeks of gestation is insufficient, and the balance of benefits and harms of screening cannot be determined 5.
Screening Methods
- Two methods are currently widely used for screening and diagnosis of GDM: a one-step approach (the 75g-Oral Glucose Tolerance Test, OGTT) and a two-step approach (the 50g Glucose Challenge Test, GCT, followed by 100g-OGTT) 3, 4.
- The 75g-OGTT is recommended for the diagnosis of GDM between 24-28 weeks of pregnancy due to its faster diagnosis time, better tolerance, and ease of remembrance 3, 4.
Early Screening
- Some studies suggest that early screening for GDM (between 16-18 weeks) may be beneficial in high-risk women, but the evidence is limited and conflicting 2, 6.
- The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for GDM in asymptomatic pregnant persons before 24 weeks of gestation 5.