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