One Step or Two Step: Which is the Best Method for GDM Screening?

BACKGROUND AND PURPOSE:

• The best method for gestational diabetes mellitus (GDM) screening remains controversial
• One-step approach: 75 g 2 hours OGTT using the IADPSG criteria
  • Recommended by: IADPSG | FIGO | WHO
• Two-step approach: 50 g 1 hour GCT followed by a 3 hours 100 g OGTT
  • Recommended by: ACOG | ADA
• Saccone et al. (The Journal of Maternal-Fetal & Neonatal Medicine, 2018) assessed the incidence of maternal and neonatal outcomes comparing one-step vs  two-step approach

METHODS:

• Systematic review and meta-analysis
• Data sources
  • Electronic database from inception until June 2018
• Inclusion criteria
  • RCTs that compared the one-step vs two-step method for screening and diagnosis of GDM
• Study design
  • Large for gestation age (LGA): Defined as birth weight >90th percentile
  • Meta-analysis was performed using the random effects model
    • Treatment effects calculated as relative risk (RR) with 95% CI
• Primary outcome
  • Incidence of LGA
• Multiple secondary outcomes included
  • Maternal complications such as preeclampsia, preterm birth, induction of labor, shoulder dystocia and cesarean delivery
  • Neonatal adverse outcomes, including neonatal hypoglycemia or hyperbilirubinemia and NICU admission  

RESULTS:

• 4 RCTs were included | Total of 2582 participants | Overall risk of bias was low
• Control groups (2-step approach) among the 4 studies
  • 2 trials: 50 g 1 hour GCT followed by 100 g 3 hours (OGTT)
  • 1 trial: 50 g 1-hour test before randomization with exclusion if glucose ≥200 mg/dL
  • 3-arm trial with two control groups (considered as 1 control group for this meta-analysis)
    • Two-step 50 g 1 hour followed by 100 g 3 hours OGTT
    • Two-step 50 g 1 hour GCT followed by 75 g 2 hours OGTT
• Management of diabetes also differed with respect to use of insulin as exclusive first line medication as well as glucose target values  
• One-step approach was associated with a lower risk of adverse perinatal outcomes, such as
  • LGA (primary outcome): 2.9% vs 6.3%; RR 0.46 (95% CI, 0.25 to 0.83)
  • NICU admission: RR 0.49 (95% CI, 0.29 to 0.84)
  • Neonatal hypoglycemia: RR 0.52 (95% CI, 0.28 to 0.95)
• The one-step approach was associated with lower mean birth weight
  • Mean difference −112.91 grams (95% CI, −190.48 to −35.33)
• There was no significant difference in the incidence of GDM
  • One step: 8.3%
  • Two step: 4.4%
  • RR 1.60 (95% CI 0.93 to 2.75)
• Authors performed a subgroup analysis removing the 3-arm trial (slightly different inclusion criteria, i.e. multiple gestations) and also differences in screening criteria compared to the other studies (Canadian Diabetes Association)
  • Incidence of GDM was increased with removal of this trial (12.6% vs 5.6%; RR 2.20)
• Subgroup analysis was only performed for GDM incidence and not perinatal outcomes

CONCLUSION:

• In this meta-analysis, the one-step approach to GDM screening was associated with better perinatal outcomes compared to the two-step approach
• The authors state that

The argument against the one-step approach has been that it increases the incidence of GDM significantly, without proven improvement in maternal and/or perinatal outcomes
Our meta-analysis of RCTs, however, provides level-1 evidence that the one-step approach significantly improves perinatal outcomes
In particular, we found a 54% reduction in the risk of LGA

Learn More – Primary Sources:

Screening for gestational diabetes mellitus: one step versus two step approach. A meta-analysis of randomized trials

Updated ACOG Guidance on Gestational Diabetes

SUMMARY:

ACOG released updated guidance on gestational diabetes (GDM), which has become increasingly prevalent worldwide.  Class A1GDM refers to diet-controlled GDM. Class A2GDM refers to the clinical scenario where medications are required. Highlights and changes from the previous practice bulletin include the following:

• Screening for GDM – One or Two Step?
• Who Should be Screened Early?
• Screening for Diabetes and Pre-Diabetes in The Postpartum Period
• What Are Glucose Target Levels?
• Diet and Exercise
• Pharmacologic Treatment
• Fetal Monitoring
• When to Deliver?

Screening for GDM – One or Two Step?

• ACOG (based on NIH consensus panel findings) supports the ‘2 step’ approach (24 – 28 week 1 hour venous glucose measurement following 50g oral glucose solution), followed by a 100g 3 hour oral glucose tolerance test (OGTT) if positive
  • Note: Diagnosis of GDM is based on 2 abnormal values on the 3 hour OGTT
    • ACOG recommends that currently there is insufficient evidence to diagnose GDM based on only one abnormal value
    • Patients with only one elevated value may require additional surveillance
• 1 step approach (75 g OGTT) on all women will increase the diagnosis of GDM but sufficient prospective studies demonstrating improved outcomes still lacking
• ACOG does acknowledge that some centers may opt for ‘1 step’ if warranted based on their population
• ADA considers either 1 step or 2 step (using Coustan Carpenter criteria) to both be valid for GDM diagnosis
• The USPSTF
  • Recommends screening for gestational diabetes in asymptomatic pregnant persons at ≥24 weeks of gestation or after (B recommendation)
  • Current evidence is insufficient to assess the balance of benefits and harms of screening for gestational diabetes in asymptomatic pregnant persons <24 weeks of gestation (I statement)

Who Should be Screened Early?

ACOG has adopted the NIDDK / ADA guidance on screening for diabetes and prediabetes which takes in to account not only previous pregnancy history but also risk factors associated with type 2 diabetes. Consider early screening in pregnancy if:

Patient is overweight with BMI of 25 (23 in Asian Americans), and one of the following

• Physical inactivity
• Known impaired glucose metabolism
• Previous pregnancy history of:
  • GDM
  • Macrosomia (≥ 4000 g)
  • Stillbirth
• Hypertension (140/90 mm Hg or being treated for hypertension)
• HDL cholesterol ≤ 35 mg/dl (0.90 mmol/L)
• Fasting triglyceride ≥ 250 mg/dL (2.82 mmol/L)
• PCOS,  acanthosis nigricans, nonalcoholic steatohepatitis, morbid obesity and other conditions associated with insulin resistance
• Hgb A1C ≥ 5.7%, impaired glucose tolerance or impaired fasting glucose | If A1C>6.5%, diagnosis of pregestational diabetes is met and GCT/GTT not needed
• Cardiovascular disease
• Family history of diabetes – 1st degree relative (parent or sibling)
• Ethnicity of African American, American Indian, Asian American, Hispanic, Latina, or Pacific Islander

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