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


  • 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


  • 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  


  • 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


  • 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

Practical obstetrics info for your women's healthcare practice

Screening for Gestational Diabetes: The ‘2 Step’ Approach


Professional organizations agree that all pregnant women should be screening for Gestational Diabetes Mellitus (GDM).  While there are varying approaches, ACOG and a consensus panel convened by the NIH have endorsed the following ‘2 step’ approach to screening for GDM:

STEP 1: All women should be screened for GDM between 24 and 28 weeks gestation with a 50g oral glucose solution followed by a 1 hour venous glucose measurement. Healthcare providers have the option of using the following values:

  • 130 or 135 mg/dL – lower cut-off threshold – which may identify women who may have GDM but also increase false positive rates
  • 140 mg/dL – higher cut-off threshold – which may limit the number of screen positive women, but may miss those with GDM

Screen earlier in pregnancy if high risk factors for GDM are identified:

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)
  • Triglyceride > 250 mg/dL (2.82 mmol/L)
  • PCOS
  • Hgb A1C ≥ 5.7%, impaired glucose tolerance or impaired fasting glucose
  • Cardiovascular disease
  • Signs/symptoms suggesting increased risk for diabetes such as acanthosis nigricans or morbid obesity)
  • Family history of diabetes – 1st degree relative
  • Ethnicity of African American, American Indian, Asian American, Hispanic, Latina, or Pacific Islander

If a patient with risk factors is tested earlier and is screen negative, the patient should still be screened again between 24-28 weeks using the 50g oral glucose load.

STEP 2: If screen positive following STEP 1,  a diagnostic test, the 100g 3 hour oral glucose tolerance test (OGTT), is recommended. A diagnosis is made if at least two values are exceeded using one of two methods:

Note: 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

National Diabetes Data Group

  • Fasting ≥ 105 mg/dL  (5.8 mmol/l)
  • 1-hour ≥ 190 mg/dL   (10.6 mmol/l)
  • 2-hour ≥ 165 mg/dL   (9.2 mmol/l)
  • 3-hour ≥ 145 mg/dL   (8.0 mmol/l)

Carpenter and Coustan

  • Fasting ≥ 95 mg/dL (5.3 mmol/l)
  • 1-hour ≥ 180 mg/dL (10.0 mmol/l)
  • 2-hour ≥ 155 mg/dL (8.6 mmol/l)
  • 3-hour ≥ 140 mg/dL (7.8 mmol/l)


GDM is a common complication of pregnancy. Aside from well-known complications associated with birth trauma and increased risk of operative delivery and preeclampsia, there may be long term complications including increased risk of obesity and diabetes later in life, although maternal obesity and excessive weight gain may be independent risk factors for macrosomia and childhood obesity. Treatment for GDM does appear to improve outcomes.  Screening all women is necessary as traditional risk factors may only detect 50% of GDM.


  • ACOG and consensus panel convened by the NIH do not recommend the ‘one step’ approach, but rather the ‘two step’ approach
  • The ‘one-step’ screening approach will result is increased diagnosis of GDM
  • Targeting obesity and improved nutrition can also address macrosomia risks

Learn More – Primary Sources:

ACOG Practice Bulletin No. 190: Gestational Diabetes Mellitus