1. Women should be screened for gestational diabetes at 24-28 gestation.
2. There are 2 different recommended testing strategies:
   1. Two-Step (most common)
      1. 50g glucose challenge
         1. Given regardless of when last meal was.
         2. Serum glucose measured at 1-hour
            1. ≥130-140 mg/dL is positive test
               1. The lower the threshold the higher sensitivity, but increased false positives
               2. The higher the threshold the higher the specificity, but with decreased sensitivity
      2. If 1st step positive, a 100g glucose challenge given
         1. Overnight fast and measured at:
            1. Fasting –> (+) if ≥ 95 mg/dL
            2. 1 hour –> (+) if ≥ 180 mg/dL
            3. 2 hour –> (+) if ≥ 155 mg/dL
            4. 3 hour –> (+) if ≥ 140 mg/dL
   2. One-Step
      1. 75 glucose challenge
         1. Given after overnight fast and measured at:
            1. Fasting –> (+) if ≥ 92 mg/dL
            2. 1 hour –> (+) if ≥ 180 mg/dL
            3. 2 hour –> (+) if ≥ 153 mg/dL

References

1. Practice Bulletin No. 137: Gestational diabetes mellitus. Obstetrics and Gynecology. 2013;122(2 Pt 1):406-16. [pubmed]
2. Hod M, Kapur A, Sacks DA. The International Federation of Gynecology and Obstetrics (FIGO) Initiative on gestational diabetes mellitus: A pragmatic guide for diagnosis, management, and care. International journal of gynaecology and obstetrics. 2015;131 Suppl 3:S173-211. [pubmed]
3. Moyer VA, . Screening for gestational diabetes mellitus: U.S. Preventive Services Task Force recommendation statement. Annals of internal medicine. 204;160(6):414-20. [pubmed]