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 

GDM Testing in Early Pregnancy 

• Best test method is unclear 
• Nonpregnant approach ‘could’ be use 
  • Fasting blood glucose followed by a 75-g glucose load and a 2-hour plasma glucose measurement
• 2 step approach (see above) is commonly used
  • Start with 50 g screening test with follow-up if initial screening test is positive  

Note: In case of a negative result in early pregnancy, GDM screening 24 to 28 weeks is still recommended | If initial 50 g screening test is positive but follow-up is negative, move on to follow-up test between 24 and 28 weeks as repeating the 50 g screening test is not necessary 

(more…)

ACOG and SMFM Both Release Guidance on Gestational Diabetes – Insulin vs Metformin for First-Line Therapy?

SUMMARY:

The SMFM released a statement on the use of metformin as a first-line alternative to insulin in women with GDM.  ACOG has also released an update to the major 2017 Practice Bulletin which also addresses this issue and still considers insulin the preferred option to treat women who are not adequately controlled with appropriate nutritional therapy.

• Both the ACOG update and SMFM statement summarize the literature, including recent meta-analyses on the comparison studies between insulin and metformin
  • Data has been conflicting based on whether non-published studies included women with type II diabetes
  • Some studies have demonstrated a higher risk for preterm birth (but lower for gestational hypertension) in the metformin group while other studies have not identified a difference in preterm birth

ACOG

• Based on current evidence, ACOG states that, consistent with ADA guidance, insulin is the ‘preferred’ approach for GDM for women not sufficiently controlled with diet and exercise
• In addition, the ACOG update states

Thus, although metformin may be a reasonable alternative approach to treat gestational diabetes, it is important to counsel women about the lack of superiority when compared with insulin, the placental transfer of the drug, and the absence of long-term data in exposed offspring. Additionally, in the aforementioned prospective trials, between 26% and 46% of women who took metformin alone eventually required insulin.

SMFM

• Upon review of the evidence, SMFM considers metformin to be a “reasonable and safe first-line pharmacologic alternative to insulin”
• More data is needed to establish long-term safety of oral agents
• Glyburide has been associated with adverse neonatal events, such as macrosomia and hypoglycemia but SMFM also acknowledges that “the evidence of benefit of one oral agent over the other remains limited”
• SMFM does acknowledge that their statement conflicts with ACOG, however

…this difference is based on the values placed by different experts and providers on the evidence available in the medical literature and is not meant to represent an exclusive course of management.

KEY POINTS:

Other ACOG Updates

One abnormal values on the 3 hour OGTT

• In the previous 2017 practice bulletin, while it was clearly stated that diagnosis of GDM is based on 2 abnormal values on the 3 hour OGTT, ACOG seemed to suggest that one abnormal value may be sufficient to make the diagnosis
• In the updated 2018 version, ACOG has clarified that statement
  • One abnormal glucose level may warrant a higher level of scrutiny, but is not sufficient for diagnosis
  • More studies are required to determine risk of adverse outcomes and who would benefit from making this a diagnostic criteria

Clarification of insulin use and dosage

• ACOG has clarified the previous practice bulletin and now states that in women who have abnormal postprandial and fasting glucose levels
  • Insulin starting dose is 0.7-1.0 units/kg daily
  • Dosage should be divided and long-acting or intermediate-acting insulin in combination with short-acting insulin should be used
• Previously, the 2017 documented stated that insulin was ‘first line’ therapy and the updated document now says ‘preferred’
  • ACOG recognizes that clinicians may assess the clinical circumstances and find the use of oral agents to be a better alternative in women (e.g., patient cannot afford insulin or feel administering the drug would be unsafe)

Macrosomia and cesarean section

• The recommendation that women with GDM should be counseled about the risks/benefits of a scheduled cesarean section if the estimated fetal weight is ≥4,500 g has been moved from ‘limited or inconsistent scientific evidence’ (Level B) to ‘consensus and expert opinion’ (Level C)

Learn More – Primary Sources:

SMFM Statement Pharmacological treatment of gestational diabetes

ACOG Practice Bulletin 190: Gestational Diabetes Mellitus

 

CONCEPTT Study: Time for Continuous Glucose Monitoring for All Pregnant Women with Type 1 Diabetes?

BACKGROUND AND PURPOSE:

1. Continuous glucose monitoring (CGM) provides contemporaneous glucose readings, thus allowing patients to adjust insulin in real-time
2. Data in non-pregnant women show benefit but conflicting data in pregnancy
3. Feig et al. (Lancet, 2017) determined the effectiveness of continuous glucose monitoring (CGM) on maternal glucose control compared to capillary glucose monitoring alone

METHODS:

• Multicenter, open-label, randomized controlled trial (2013-2016)
• 31 hospital centers in Canada, England, Scotland, Spain, Italy, Ireland, and the USA
• Women aged 18 to 40 years, with type 1 diabetes for a minimum of 1 year, receiving intensive insulin therapy, and pregnant or planning pregnancy
  • Live singleton fetus confirmed by ultrasound
  • ≤13 weeks and 6 days’ gestation
  • Pregnant: HbA1c between 6.5–10.0% (48–86 mmol/mol)
  • Planning for pregnancy: 7.0–10.0% (53–86 mmol/mol)
• Ran 2 trials in parallel for (1) pregnant and (2) planning pregnancy
• In both trials, participants were assigned to the following cohorts
  • Receive CGM in addition to capillary glucose monitoring
  • Receive capillary glucose monitoring
• Randomization was stratified by insulin delivery and baseline HbA1c
• Primary outcome was change in HbA1c
  • at 34 weeks’ gestation in pregnant participants
  • at 24 weeks for planning pregnancy participants
• Secondary outcomes included obstetric and neonatal health outcomes

RESULTS:

• 325 women were randomized
• When comparing pregnant CGM users to capillary monitored group, CGM users
  • had a slightly greater change in HbA_1c (mean difference -0.19%; 95% CI -0.34 to -0.03; p=0.0207)
  • Spent more time in target range (68% vs 61%; 0.0034)
  • Spent less time hyperglycemic range (27% vs 32%; p= 0.0279)
  • Had comparable hypoglycemic episodes
  • Spent comparable amount of time in hypoglycemic range (3% vs 4%, respectively)
• Neonatal outcomes in CGM users were significantly improved
  • Lower incidence of large for gestational age (odds ratio [OR] 0.51, 95% CI 0.28 – 0.90; p=0.0210)
  • Fewer NICU admissions lasting more than 24 h (OR 0.48; 95% CI 0.26 – 0.86; p=0.0157)
  • Fewer incidences of neonatal hypoglycemia (OR 0.45; 95% CI 0.22 to 0.89; p=0.0250)
  • 1-day shorter length of hospital stay (p=0.0091)
• There was no apparent benefit of CGM for women planning pregnancy
• CGM users had significantly more adverse skin reactions during trials (48% CGM vs 8% control during pregnancy; 44% CGM vs 9% control planning pregnancy)
• Data was generalizable across centers

CONCLUSION:

• CGM during pregnancy in patients with type 1 diabetes is linked to improved neonatal outcomes, likely because of better maternal glycemic control and reduced maternal hyperglycemia
• Number needed to treat (NNT) with CGM
  • 6 pregnant women NNT to prevent one NICU admission
  • 6 pregnant women NNT to prevent one large for gestational age
  • 8 pregnant women NNT to prevent one case of neonatal hypoglycemia
• The authors conclude that guidelines in type 1 diabetes in pregnancy should be revised to recommend offering CGM to pregnant women with type 1 diabetes using intensive insulin therapy in the first trimester

Learn More – Primary Sources:

Continuous glucose monitoring in pregnant women with type 1 diabetes (CONCEPTT): a multicentre international randomised controlled trial.