Low Risk: Blood glucose testing not routinely required if all the following are present:
Member of an ethnic group with a low prevalence of GDM No known diabetes in first-degree relatives
No history of abnormal glucose metabolism No history of poor obstetrical outcome
Average Risk: Perform blood glucose testing at 24 to 28 weeks using either:
Two-step procedure: 50-g oral glucose challenge test (GCT), followed by a diagnostic 100-g OGI for those meeting the threshold value in the GCT One-step procedure: diagnostic 100-g OGTI performed on all subjects
High Risk: Perform blood glucose testing as soon as feasible, using the procedures described above, if one or more of these are present:
Strong family history of type 2 diabetes
Previous history of GDM, impaired glucose metabolism, or glucosuria
If GDM is not diagnosed, blood glucose testing should be repeated at 24 to aCriteria of the Fifth Intenational Workshop-Conference on Diabetes. GDM = gestational diabetes mellitus; OGTI = oral glucose tolerance test.
Reproduced with permission from Metzger BE, Coustan DR, the Organizing Committee:
Summary and recommendations of the Fourth International Workshop-Conference on Gestational Diabetes Mellitus, Diabetes Care. 1998 Aug; 21 SuppIn2:B161n-B167.
TABLE 57-13. Diagnosis of GDM Using Threshold women not known to have glucose intolerance earlier in preg nancy. This 50-g screening test is followed by a dianostic 100-g,
Tolerance Testa,b 3-hour oral glucose tolerance test (OGT) if screening results meet or exceed a predetermined plasma glucose concentration.
For the 50-g screen, the plasma glucose level is measured 1 hour ater a 50-g oral glucose load without regard to the time
Fasting 105 5.8 95 5.3 of day or time oflast meal. In a recent review, the pooled sensitiv1-hr 190 10.6 180 2-hr 165 9.2 155 8.6 ity for a threshold of 140 mg/dL ranged from 74 to 83 percent depending on 100-g thresholds used for diagnosis (van Leeuwen, 3-hr 145 8.0 140 2012). Sensitivity estimates for a 50-g screen threshold of 135 aThe test should be performed when the patient is fasting. bTwo or more of the venous plasma glucose concentra mg/dL improved only slightly to 78 to 85 percent. Importantly, speciicity dropped from a range of 72 to 85 percent for 140 mg/dL to 65 to 81 percent for a threshold of 135 mg/dL. Using a threshold of 130 mg/dL marginally improves sensitivity with a further decline in speciicity (Donovan, 2013). That said, in the absence of clear evidence supporting one cutof value over another, the American College of Obstetricians and Gynecolo gists (2017a) sanctions using anyrone of the three 50-g screen thresholds. At Parkland Hospital, we continue to use 140 mg/dL as the screening threshold to prompt the 100-g test.