First prenatal visit. Due to the rise of obesity and type 2 diabetes, there is an increasing number of women with T2DM who become pregnant. Women with risk factors for diabetes (see post I) should be tested for diabetes using criteria for individuals outside pregnancy. According to the result of this test, there are 3 possibilities:
- Pregnant women who meet diagnostic criteria for type 2 diabetes (the same criteria for individuals outside pregnancy) should be considered as diabetes complicating pregnancy (i.e. diabetes previous to pregnancy, mostly T2DM) andg managed accordingly.
- Women who do not meet diagnostic criteria for diabetes, but the lower criteria for gestational diabetes, should be diagnosed of Gestational Diabetes and managed accordingly. The problem is that diagnostic criteria for GDM (both IADPSG and the 2-step approach) are not derived from 1st trimester data, so diagnosis of GDM in 1st trimester is not validated and not evedence-based.
- The rest of women who do not meet any diagnostic criteria are euglycemic and should be evaluated later in pregnancy at week 24-28 for GDM.
Week 24-28. The HAPO study evidenced that any degree of hyperglycemia in week 24-28 was associated to worse pregnancy outcomes. For most complications there was no threshold, and risk increases even in glycemic levels previously considered as normal. According to this, there are currently two diagnostic strategies for GDM detection:
- Two-Step Stategy. In 2013 the NIH convened a consensus converence resulting in recommendation of a 2 step strategy:
- 50 g OGTT with cut point of 130, 135 or 140 mg/dL, no aggreement according to different sensitivities and specificities ov every value.
- If positive, 100 g OGTT, diagnostic if 2 pathologic cut-points of Carpender and Coustan Criteria:
- Basal: 95 mg/dL
- 1h: 180 mg/dL
- 2h: 155 mg/dL
- 3h: 140 mg/dL
- The National Diabetes Data Group defends different cut points of 95-190-165-145 mg/dL, according to different interpretation of conversion from the original O'Sullivan values. The Americal College of Obstetricians and Gynecologists (ACOG) accepts either cut-off values, but with only one pathologic point needed for diagnostic. A1c measurement is not accurate in diagnosis in this setting.
- One-Step Stragegy. Following the results of HAPO study, the International Association of the Diabetes and Pregnancy Study Group (IADPSG) chose as threshold those glycemic points (mg/dL) associated to 1,75 times the odds for pregnancy outcomes in a 75 g OGTT in three points: basal (92), 1h (180) and 2 hours (153). Diagnosis is made if at least one point is pathologic. This strategy has as a consequence an increase the prevalence of GDM from 5-6% to 15-20%. This approach is based in the fact that treating glycemic values below the threshold of classical GDM showed modest benefits in macrosomia and preeclapsia. But there are no RCT evaluating treat vs. no treat in women meeting IADPSG but not 2-step criteria. So, this strategy is not universally accepted.
There is controversy about which of both strategies are more cost-effective. The 2 step approach has proved to reduce macrosomia, and shoulder distocia without increasing small-for-gestational-age births. Future research is needed to clarify which criteria are more appropriate.
