Table 5—

Screening for and diagnosis of GDM

Carry out GDM risk assessment at the first prenatal visit.
Women at very high risk for GDM should be screened for diabetes as soon as possible after the confirmation of pregnancy. Criteria for very high risk are:
  • severe obesity

  • prior history of GDM or delivery of large-for-gestational-age infant

  • presence of glycosuria

  • diagnosis of PCOS

  • strong family history of type 2 diabetes

Screening/diagnosis at this stage of pregnancy should use standard diagnostic testing (Table 2).
All women of greater than low risk of GDM, including those above not found to have diabetes early in pregnancy, should undergo GDM testing at 24–28 weeks of gestation. Low risk status, which does not require GDM screening, is defined as women with ALL of the following characteristics:
  • age <25 years

  • weight normal before pregnancy

  • member of an ethnic group with a low prevalence of diabetes

  • no known diabetes in first-degree relatives

  • no history of abnormal glucose tolerance

  • no history of poor obstetrical outcome

Two approaches may be followed for GDM screening at 24–28 weeks:
  1. Two-step approach:

  2. Perform initial screening by measuring plasma or serum glucose 1 h after a 50-g oral glucose load. A glucose threshold after 50-g load of ≥140 mg/dl identifies ∼80% of women with GDM, while the sensitivity is further increased to ∼90% by a threshold of ≥130 mg/dl.

  3. Perform a diagnostic 100-g OGTT on a separate day in women who exceed the chosen threshold on 50-g screening.

  4. One-step approach (may be preferred in clinics with high prevalence of GDM): Perform a diagnostic 100-g OGTT in all women to be tested at 24–28 weeks.

The 100-g OGTT should be performed in the morning after an overnight fast of at least 8 h.
To make a diagnosis of GDM, at least two of the following plasma glucose values must be found:
  • Fasting: ≥95 mg/dl

  • 1 h: ≥180 mg/dl

  • 2 h: ≥155 mg/dl

  • 3 h: ≥140 mg/dl