Gestational Diabetes Mellitus: Screening and Management

SUMMARY:

Gestational diabetes mellitus (GDM) has become increasingly prevalent worldwide.  Class A1GDM refers to diet-controlled GDM. Class A2GDM refers to the clinical scenario where medications are required. The following synopsis highlights key practice points from various professional organizations. 

• 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 – First or Second Trimester?

• ACOG supports the ‘2 step’ approach (24 to 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
• ACOG does not recommend routine screening for GDM <24 weeks 
• 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)
• ACOG and ADA prefer use of Carpenter and  Coustan vs national Diabetes Data Group (NDDG) criteria because the higher NDDG thresholds may result in missed opportunities to treat patients would would benefit from GDM diagnosis
  • Fasting blood sugar: <95 mg/dL (5.3 mmol/L)
  • 1 hour blood sugar: <180 mg/dL (10.0 mmol/L)
  • 2 hour blood sugar: <155 mg/dL (8.6 mmol/L)
  • 3 hour blood sugar: <140 mg/dL (7.8 mmol/L) 

Who Should be Screened Early?

The ACOG update is based on ADA criteria | Consider early screening in pregnancy if patient is overweight with BMI of ≥25 kg/m3 (23 in Asian Americans), and one or more of the following

• Physical inactivity
• Family history of diabetes – 1st degree relative (parent or sibling)
• Black, Hispanic, Native American, Asian American, or Pacific Islander
• Previous pregnancy history of
  • GDM
  • Macrosomia (≥ 4000 g)
• 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
• Conditions associated with insulin resistance (e.g., acanthosis nigricans, morbid obesity)
• 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
• HIV
• 35 years or older 
• Other factors suggestive of increased risk for pregestational diabetes

Note: The ADA (2025) uses 130/80 as the BP threshold for hypertension diagnosis 

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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